You affect the world around you primarily by using actions, which produce effects. Actions are most closely measured and restricted during the encounter mode of play, but even when it isn't important for you to keep strict track of actions, they remain the way in which you interact with the game world. There are four types of actions: single actions, activities, reactions, and free actions.

Action Icon Key

These icons appear in stat blocks as shorthand for each type of action.

[one-action]         Single Action
[two-actions]        Two-Action Activity
[three-actions]        Three-Action Activity
[reaction]         Reaction
[free-action]         Free Action

Single actions can be completed in a very short time. They're self-contained, and their effects are generated within the span of that single action. During an encounter, you get 3 actions at the beginning of your turn.

Activities usually take longer and require using multiple actions, which must be spent in succession. Stride is a single action, but Sudden Charge is an activity in which you use both the Stride and Strike actions to generate its effect.

Reactions have triggers, which must be met for you to use the reaction. You can use a reaction anytime its trigger is met, whether it's your turn or not. In an encounter, you get 1 reaction each round. Outside of encounters, your use of reactions is more flexible and up to the GM. Reactions are usually triggered by other creatures or by events outside your control.

Free actions don't cost you any of your actions per turn, nor do they cost your reaction. A free action with no trigger follows the same rules as a single action (except the action cost), and a free action with a trigger follows the same rules as a reaction (except the reaction cost).

Activities

An activity typically involves using multiple actions to create an effect greater than you can produce with a single action, or combining multiple single actions to produce an effect that's different from merely the sum of those actions. In some cases, usually when spellcasting, an activity can consist of only 1 action, 1 reaction, or even 1 free action. 

An activity might cause you to use specific actions within it. You don't have to spend additional actions to perform them—they're already factored into the activity's required actions.

You have to spend all the actions of an activity at once to gain its effects. In an encounter, this means you must complete it during your turn. If an activity gets interrupted or disrupted in an encounter, you lose all the actions you committed to it.

Exploration and Downtime Activities

Outside of encounters, activities can take minutes, hours, or even days. These activities usually have the exploration or downtime trait to indicate they're meant to be used during these modes of play. You can often do other things off and on as you carry out these activities, provided they aren't significant activities of their own. For instance, if you're Repairing an item, you might move around to stretch your legs or have a brief discussion—but you couldn't also Decipher Writing at the same time.

If an activity that occurs outside of an encounter is interrupted or disrupted, as described in Disrupting Actions below, you usually lose the time you put in, but no additional time beyond that.

Actions with Triggers

You can use free actions that have triggers and reactions only in response to certain events. Each such reaction and free action lists the trigger that must happen for you to perform it. When its trigger is satisfied—and only when it is satisfied—you can use the reaction or free action, though you don't have to use the action if you don't want to.

There are only a few basic reactions and free actions that all characters can use. You're more likely to gain actions with triggers from your class, feats, and magic items.

Limitations on Triggers

The triggers listed in the stat blocks of reactions and some free actions limit when you can use those actions. You can use only one action in response to a given trigger. For example, if you had a reaction and a free action that both had a trigger of “your turn begins,” you could use either of them at the start of your turn—but not both. If two triggers are similar, but not identical, the GM determines whether you can use one action in response to each or whether they're effectively the same thing. Usually, this decision will be based on what's happening in the narrative.

This limitation of one action per trigger is per creature; more than one creature can use a reaction or free action in response to a given trigger.

Other Actions

Sometimes you need to attempt something not already covered by defined actions in the game. When this happens, the rules tell you how many actions you need to spend, as well as any traits your action might have. For example, a spell that lets you switch targets might say you can do so “by spending a single action, which has the concentrate trait.” Game masters can also use this approach when a character tries to do something that isn't covered in the rules.

Gaining and Losing Actions

Conditions can change the number of actions you can use on your turn, or whether you can use actions at all. The slowed condition, for example, causes you to lose actions, while the quickened condition causes you to gain them. Whenever you lose a number of actions—whether from these conditions or in any other way—you choose which to lose if there's any difference between them. For instance, the haste spell makes you quickened, but it limits what you can use your extra action to do. If you lost an action while haste was active, you might want to lose the action from haste first, since it's more limited than your normal actions.

Some effects are even more restrictive. Certain abilities, instead of or in addition to changing the number of actions you can use, say specifically that you can't use reactions. The most restrictive form of reducing actions is when an effect states that you can't act: this means you can't use any actions, or even speak. When you can't act, you don't regain your actions and reaction on your turn. 

Disrupting Actions

Various abilities and conditions, such as an Attack of Opportunity, can disrupt an action. When an action is disrupted, you still use the actions or reactions you committed and you still expend any costs, but the action's effects don't occur. In the case of an activity, you usually lose all actions spent for the activity up through the end of that turn. For instance, if you began a Cast a Spell activity requiring 3 actions and the first action was disrupted, you lose all 3 actions that you committed to that activity.

The GM decides what effects a disruption causes beyond simply negating the effects that would have occurred from the disrupted action. For instance, a Leap disrupted midway wouldn't transport you back to the start of your jump, and a disrupted item hand off might cause the item to fall to the ground instead of staying in the hand of the creature who was trying to give it away.

In-Depth action Rules

These rules clarify some of the specifics of using actions.

Simultaneous Actions

You can use only one single action, activity, or free action that doesn't have a trigger at a time. You must complete one before beginning another. For example, the Sudden Charge activity states you must Stride twice and then Strike, so you couldn't use an Interact action to open a door in the middle of the movement, nor could you perform part of the move, make your attack, and then finish the move. 

Free actions with triggers and reactions work differently. You can use these whenever the trigger occurs, even if the trigger occurs in the middle of another action.

Subordinate Actions

An action might allow you to use a simpler action in a different circumstance or with different effects. This subordinate action still has its normal traits and effects, but is modified in any ways listed in the larger action. For example, an activity that tells you to Stride up to half your Speed alters the normal distance you can move in a Stride. The Stride would still have the move trait, would still trigger reactions that occur based on movement, and so on. The subordinate action doesn't gain any of the traits of the larger action unless specified. The action that allows you to use a subordinate action doesn't require you to spend more actions or reactions to do so; that cost is already factored in.

Using an activity is not the same as using any of its subordinate actions. For example, the quickened condition you get from the haste spell lets you spend an extra action each turn to Stride or Strike, but you couldn't use the extra action for an activity that includes a Stride or Strike. As another example, if you used an action that specified, “If the next action you use is a Strike,” an activity that includes a Strike wouldn't count, because the next thing you are doing is starting an activity, not using the Strike basic action.