Just like real life CL, top 2 teams qualify for knockout stages, then its knockout matches over 2 legs, from Last 16, Quarter-Final, Semi-Final and then the final is a one-off venue.
Tie breaker rules in group stages is Goal Difference, then Goals scored.
In 2 legged matches. If its a tie over both games away goal rule applies (most away goals wins) then extra time and penalties.
In the final, 90 minutes, if equal extra-time and penalties.