Action Points
In order to perform an ability, you must have enough Action Points (AP) to do so. Action points are a global pool which apply to all skills.
Each player starts an encounter with 10 AP.
In an encounter, all of your abilities will cost certain amounts of AP.
Let's say you start with 10 AP, and you use an ability which costs 2 AP. The player performs the ability, and then subtracts 2 AP, which brings them down to 8.
AP do not restore under normal circumstances. Critical successes can restore AP, as well as certain abilities and perks.
Standard actions like movement do not cost AP. It is up to the DM's discretion to decide which actions cost AP.