During an encounter, you get 3 actions and 1 reaction per
turn. Icons indicate whether your abilities take a single action
[one-action], 2 actions
[two-actions], 3 actions
[three-actions], a reaction
[reaction], or a free action
[free-action].
Reactions have
Triggers, allowing you to take them whenever they come up. The
Ready basic action lets you prepare to use a single action as a reaction. Free actions can have triggers like reactions; a free action with no trigger can be used like a single action, but don't cost any of your actions for the turn.
The most important actions to learn are the
basic actions. Specialty basic actions come up less frequently, and you typically won't look them up until you need them.
Speaking normally doesn't take an action.
Related: Activities,
disrupting actions