Buttons can be either on the card or on the board level. Right where you need them.
Card buttons can perform all the most usual actions (and sequences with multiple actions) on the card that is currently open.
Board buttons can perform actions that affect the board (e.g. create a list) or affect multiple cards (e.g. archive all the cards with a certain label). They can also sort the cards in a list by due date, title, votes, labels or the value of a custom field.