When you want to do something in the game, you tell the DM what you want to accomplish, and then the DM assigns a difficulty class and tells you what modifiers apply to your check roll. While this is enough to get started, the game provides more detailed rules to determine what kinds of actions that you can perform at what times.
There are multiple kinds of actions that you can perform in the game, divided into how long they take, how often you can perform them, and how much training they require.
Free actions take almost no time or effort to perform, like noticing something that you’re looking at or speaking a word or two. During an encounter, you can perform any number of free actions (within reason) on any creature's turn, unless some condition prevents you from doing so.
Immediate actions take a half second or so of your concentration, like drinking from a cup or picking up keys that are lying on the table. During an encounter, you can perform one immediate action, reaction or interrupt during your turn, and one immediate reaction or interrupt during each other creature's turn, unless some condition prevents you from doing so.
Move actions take enough concentration to watch where your feet are going, but not much more. As you would expect, move actions typically let you move around from place to place, but other move actions use your legs or body to do other things. During an encounter, you can perform one move action during each of your own turns, unless some condition prevents you from doing so. If you are able to perform a move action, you can use it to perform an immediate action instead.
Standard actions take several seconds of your full attention to pull off, like aiming and firing a weapon, threading a needle, or working the controls of a complex machine. During an encounter, you can perform one standard action during each of your own turns, unless some condition prevents you from doing so. If you are able to perform a standard action, you can use it to perform a move action or an immediate action instead.
Finally, Extended actions take more than a few seconds to perform, and hence tend to keep you committed for more time than the tempo of combat allows for.
At-Will actions can be free actions, immediate actions, move actions, standard actions or extended actions; the key qualification is that you can perform an at-will action whenever you feel like. Thus, if something is an “at-will move action”, that means that whenever it’s your turn and you feel like it, you can decide to spend as much effort as it takes to walk across the room to perform that action.
Per-Encounter actions, also called per-encounter feats, tend to be fatiguing, and so can only be used a limited number of times before you need to sit down and rest. Like at-will actions, per-encounter actions can be free, immediate, move, standard or extended.
Daily actions, also called daily feats, tend to be epic feats that take a good deal out of you, and so can only be used a limited number of times per day before you need a full night’s sleep to recharge. Like at-will and per-encounter actions, daily actions can be free, immediate, move, standard or extended.
Some actions are simpler to perform than other actions. A basic action can be performed whether or not you have proficiency in the relevant skill or weapon, and can sometimes be performed in conjunction with another action or technique.
Some actions require proficiency to perform. If you are not proficient in the skill or weapon proficiency used to perform the action, you may only attempt the action as a stunt, and you grant advantage to all enemies while attempting it.
Some particularly difficult actions require expertise to perform. If you are not proficient in the skill or weapon proficiency used to perform the action, you may not even attempt the action. If you do not have expertise, but do have proficiency, you may only attempt the action as a stunt, and you grant advantage to all enemies while attempting it.
Action Description BlocksEdit
Whenever these rules wish to describe an action that you may perform, they will use an action description block. An action description block looks like this:
You must have a drink in your hand.
When you perform this action, you may stop and not take the drink if you notice that it tastes odd.
You take a drink from the drink in your hand.
The first line, in bold, is the name of the action - in this case, “Take a Drink”. This means that when you want your character to do this action, you tell the DM “I’m going to Take a Drink” so he knows what’s going on and can react appropriately.
The next line, in italics, is the action’s type and keywords. This is two blocks, separated by an asterisk. The first block tells you when you can perform the action (in this case, at-will), how complicated the action is (in this case, it’s an immediate action), and whether it’s an Action (which you can do any time on your turn) or a Reaction or Interrupt (which you can do on your or other players’ or NPC’s turns, but only in response to specific triggers).
The next lines will list special circumstances around performing the action, such as ‘Prerequisites’, ‘Requirements’, ‘Triggers’ or ‘Special’ blocks. A Prerequisite is something you need to have before you can even learn to do the action - in this case, taking a drink has no prerequisites. A requirement or trigger is a need that must be met before you can perform the action - in this case, it is a Requirement that you have a drink in your hand in order to take a drink, which makes perfect sense. A Special block just tells you some special rules or circumstances around this action that don’t fit into any other category, such as the fact that you can decide to stop taking the drink before it affects you if it tastes odd.
The next lines will list what happens when you perform the action. Each of these lines will say ‘Effect’, ‘Check’, ‘Target’, ‘Save’, ‘Success’, ‘Failure’, ‘Hit’ or ‘Miss’, and will be listed in the order that they occur. An ‘Effect’ block always happens when you perform the action; just read the line and assume that that effect occurs. A ‘Check’ or ‘Target’ line means that you must make some kind of check at this step, while a ‘Save’ means you must make a saving throw. ‘Target’ lines have you make a choice, usually selecting a particular creature or area, before making the check; the check’s DC will be based on the target that you choose. Finally, ‘Success’ and ‘Hit’ lines only occur if you succeed at the last check that you made, while ‘Failure’ and ‘Miss’ lines only occur if you didn’t succeed at the last check that you made.