Chapter 1: Introduction / Format of Rules Elements / Understanding Actions / Free Actions wrote:
Source
Core Rulebook pg. 17 1.1
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.