If you're on phone, tap "?" in menu. Visit old guides or even Google it, since these are the fundamental know-tos of the game.

Well, it works as any other two legged competition, where they who've scored most goals when totalling both legs progresses. If there's a tie then those who've scored most goals at the away stadium progresses. If still there's a tie, then the team with most goals scored in extra time progresses. If both sides score AET then away side progresses (since they've more away goals). If no goals are scored AET, penalties take place, where each team has five chances to score. If the score's equal after 5 shots, the game goes into sudden death.
Are you American?