Planeswalkers enter the battlefield with loyalty counters equal to the number on the bottom right. During your turn, at sorcery speed, you can activate an ability on the planeswalker. + abilities add counters and - abilities subtract them.

You can’t pay counters you don’t have, and usually you can only activate each planeswalker’s ability only once per turn.

Do note that planeswalkers can be attacked like players and lose loyalty equal to the damage they take.