Sustain
Single action that extends a sustained-duration effect (typically from spells or magic items) until the end of your next turn, or maintains effects up to 10 minutes if no duration...
Concentrate
Choose one of your effects that has a sustained duration or lists a special benefit when you Sustain it. Most such effects come from spells or magic item activations. If the effect has a sustained duration, its duration extends until the end of your next turn. (Sustaining more than once in the same turn doesn't extend the duration to subsequent turns.) If an ability can be sustained but doesn't list how long, it can be sustained up to 10 minutes.
An effect might list an additional benefit that occurs if you Sustain it, and this can even appear on effects that don't have a sustained duration.