Your team is ahead of the guests. In your home, our score was 1: 1, so I got an away goal, right? Go back to my home and score 0-0, so our total score is 1: 1. Right? In this case, it depends on who scores more away goals. I scored an away goal, and your away goal was zero, so you were eliminated.
Similarly, you pick up the host first, and then pick up the guests. Your home 1: 1, my home 2: 2, so the total score is 3: 3. Watching away goals, I scored one away (your home) and you scored two away (my home), so you scored more away than me. I was eliminated.
If you draw twice and score the same goal away from home, you will play overtime. Note that extra-time away goals also count. Let me give you another example. The score is 1: 1 at your home, and 1 at my home. In this way, both teams scored 1 away goal, with a total score of 2: 2 and a draw. Just 30 minutes (first half 15 minutes), we each scored a goal in overtime and the game became 2: 2. Add your 1: 1, and the total score is 3: 3. You will have two away goals (regular season 1, overtime 1), so you will eliminate me.
If you don't see who scored more away goals in overtime, it will be a penalty shoot-out. You got it.