3-bet from the button

Someone opened before you and you're on the button, the best position. You have three options: re-raise (3-bet), call (cold-call), or fold.

Playing last postflop is a huge edge, so you can continue with plenty of hands. You re-raise your best hands for value and some bluffs; you call hands that play well in position; and you fold the rest. The looser the opener (CO > HJ > UTG), the wider you play.