What is the format of the Champions League after the group stage?

knockout stage

how does the knockout stage work? they play at each home venue, right? is it aggregate score, so we should just pretend it is a 180 minute match? if the score is tied, then the road team with more goals wins? what if it is a tie after that? penalty kicks? any OT periods?

The KO stage is like any other KO format competition i.e. World Cup, Euro Championships.

The 2 teams drawn to face each other at this stage (last 16) play 2 legs (games), one each at their home ground. If the aggregate score over the 2 legs is tied, the team that progresses is the team that scored the most away goals over those 2 legs. If this is also equal, the 2nd matchup carries on over the 90 mins into 30 mins of extra time (2 x 15 min halves), and then if there is still no winner, a penalty shoot-out is used to decide which team moves onto the next KO phase of the competition.

Hopefully this clears things up GooGooDooDoo

P.S. I'm really looking forward to the AC Milan v Man Utd game