Champions League is a knockout tournament where you are matched up with 32 top managers who finished top 4 last season.

The Champions League starts on day 3 (Wednesday) in the season and ends with the final being played on Day 13 (Saturday).

The Champions League starts with a group stage. From day 3 to day 6 in the season you play 6 matches against three opponents you have been matched in a group with.
The first three days in the group stage you play one home and one away match. The home matches can be kicked off instanly, while you have to wait for your opponent to kick off the away matches. If you opponent does not kick off your away match before 8PM CET (GMT +1) you can also kick off the matches yourself - just like in the league.
Day 6 in the season has no matches but servers as a catch up day where all managers can play their matches if not played yet.
The top 2 in each group will advance to the knockout stage.

On day 7 (Sunday) in the season the knockout stage starts. 

In the knockout stage you play a home match and an away match against the team you have been drawn against over 2 days. The best team over the two matches will proceed to the next round. 

If the two matches have ended with the exact same result, the winner will be found by player extra time (2x15 mins) and if a winner still isn't found a penalty shoot out will decide who goes through to the next round.

If the aggeragate score is even but results are different (e.g. 2-0 and 1-3 = 3-3 in total). The winner is found by looking at with team has scored most goals in their away match.

If matches are unplayed after the 2nd leg match day, the home team will lose 0-3 by forfeit to find a winner who will progress to the next round.