Source Player Core pg. 406
Characters and their adversaries affect the galaxy of Starfinder by using actions and producing effects. This is especially the case during encounters, when every action counts. When you use an action, you generate an effect. This effect might be automatic, but sometimes actions necessitate that you roll a die, and the effect is based on what you rolled.
Throughout this book, you will see special icons to denote actions.
Single actions use this symbol: [one-action]. They're the simplest, most common type of action. You can use three single actions on your turn in an encounter, in any order you see fit.
Reactions use this symbol: [reaction]. These actions can be used even when it's not your turn. You only get one reaction per encounter round, and you can use it only when its specific trigger is fulfilled. Often, the trigger is another creature's action.
Free actions use this symbol: [free-action]. Free actions don't require you to spend any of your three single actions or your reaction. A free action might have a trigger like a reaction does. If so, you can use it just like a reaction—even if it's not your turn. However, you can use only one free action per trigger, so if you have multiple free actions with the same trigger, you have to decide which to use. If a free action doesn't have a trigger, you use it like a single action, just without spending any of your actions for the turn.
These rules clarify some of the specifics of using 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 Double Tap activity states you must Aim and then make two ranged Strikes, so you couldn't use an Interact action to open a door in the middle of the Strikes.
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.
An action might allow you to use a simpler action— usually one of the Basic Actions—in a different circumstance or with different effects. This subordinate action still has its normal traits and effects, but it's 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 isn't 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're doing is starting an activity, not using the Strike basic action.
As long as you can act, you can also speak. You don't need to spend any type of action to speak, but because a round represents 6 seconds of time, you can usually speak at most a single sentence or so per round. Special uses of speech, such as attempting a Deception skill check to Lie, require spending actions and follow their own rules. All speech has the auditory trait. If you communicate in some way other than speech, other rules might apply. For instance, using sign language is visual instead of auditory.
Activities are special tasks that you complete by spending one or more of your actions together. Usually, an activity uses two or more actions and lets you do more than a single action would allow. You have to spend all the actions an activity requires for its effects to happen. Spellcasting is one of the most common activities, as most spells take more than a single action to cast.
Activities that use two actions use this symbol: [two-actions]. Meanwhile, activities that use three actions use this symbol: [three-actions]. There are also special activities, such as spells you can cast in an instant, which use a free action or a reaction.
All tasks that take longer than a turn are activities. If an activity is meant to be done during exploration, it has the exploration trait. An activity that takes a day or more of commitment and that can be done only during downtime has the downtime trait.
◆◆ Two Actions
Basic actions represent common tasks like moving around, attacking, and helping others. As such, every creature can use basic actions except in some extreme circumstances, and many of those actions are used very frequently. Most notably, you'll use Interact, Step, Stride, and Strike a great deal. Many feats and other actions call upon you to use one of these basic actions or modify them to produce different effects. For example, a more complex action might let you Stride twice, and a large number of activities include a Strike. An action or activity might also modify a basic action, such as having you Stride up to half your Speed.
Actions that are used less frequently but are still available to most creatures are presented in Specialty Basic Actions starting on page 418. These typically have requirements that not all characters are likely to meet, such as wielding a shield, having a burrow Speed, or falling through the air.
In addition to the actions in these two sections, the actions for spellcasting can be found on pages 299–300, and the actions for using magic items appear on page 220 of GM Core.
Delay and Ready: If you want to change when you take actions, two basic actions let you do so. Delay shifts your entire turn later in the round, and Ready lets you prepare to take one specific action when a trigger you choose is met.
Aid [↩] DC 15 check to give a +1 circumstance bonus to assisted skill check or attack roll (crit success: +2, +3 if master, +4 if legendary).
Crawl [◆] (move) Move 5 feet while prone.
Delay [◇] Select this when your turn begins; take your turn later.
Drop Prone [◆] (move) Fall prone.
Escape [◆] (attack) Attempt to get free when grappled, restrained, or immobilized. Use unarmed attack modifier, Acrobatics, or Athletics.
Interact [◆] (manipulate) Grab an object, open a door, draw an item, or do a similar action.
Leap [◆] (move) Jump horizontally 10 feet (15 feet if your Speed is 30 feet or more), or vertically 3 feet and horizontally 5 feet.
Ready [◆◆] (concentrate) Prepare to take a single action or free action as a reaction with a trigger you designate.
Release [◇] (manipulate) Release something you're holding without triggering reactions.
Seek [◆] (concentrate, secret) Scan an area for signs of creatures or objects using Perception.
Sense Motive [◆] (concentrate, secret) See if a creature is lying.
Stand [◆] (move) You stand up from prone.
Step [◆] (move) Move 5 feet without triggering reactions.
Stride [◆] (move) Move up to your Speed.
Strike [◆] (attack) Attack with a weapon or unarmed attack.
Take Cover [◆] Gain cover, or get greater cover if you have cover.
These actions are useful under specific circumstances. The Arrest a Fall, Burrow, and Fly actions require you to have a special movement type (page 420). The climb and swim Speeds use the corresponding actions from the Athletics skill (pages 234–235).
Arrest a Fall [↩] Use Acrobatics to slow your fall while flying.
Avert Gaze [◆] Get a +2 circumstance bonus against visual abilities.
Burrow [◆] (move) Move up to your burrow Speed.
Dismiss [◆] (concentrate) End a spell effect or magic item effect.
Fly [◆] (move) Move up to your fly Speed. Moving upward counts as traveling through difficult terrain. You can move straight down 10 feet for every 5 feet of movement you spend. If you're airborne at the end of your turn and didn't Fly this round, you fall.
Grab an Edge [↩] (manipulate) Try to catch something to stop a fall.
Mount [◆] (move) Get on an allied animal bigger than you to ride it.
Point Out [◆] (auditory, manipulate, visual) Reveal unobserved creature.
Raise a Shield [◆] Put up a shield to get its bonus to AC.
Sustain [◆] (concentrate) maintain an effect with a sustained duration until the end of your next turn.