Today, Wednesday January 29, is the final day in the Champions League's League Phase, and there are many things at stake for most of the teams. While two teams (Barcelona and Liverpool) have secured their direct qualification for the round of 16, and nine teams are already eliminated, most still don't know which place they will finish. And the trick here is that most don't depend solely on themselves, but on other teams' results, which is why all 18 games are played at the same time, on Wednesday at 21:00 CET (20:00 in the UK).
For example, there are six teams with 13 points (ranked 8-13) and at least one of them will get a spot in the top 8 (granting direct qualification for the round of 16): Bayer Leverkusen, Aston Villa, AS Monaco, Feyenoord, Lille, and Brest. And the latter three are tied with the same goal difference (+2), meaning they are ranked depending on goals scored, away goals scored, wins or number of away wins.
For nine teams in particular, the situation is more critical because their access to the knockout play-off depend on winning or losing. That includes Paris Saint-Germain or Manchester City, who could be in real trouble if they lose, although, in the case of teams with ten points (Benfica, PSG, Sporting CP and Stuttgart) they could still pass even if they loose if Man City or Shaktar Donestk don't win.
Confused? The UEFA website has a result simulator to see how you team would go up and down depending on everyone's results. The cool thing is that you can use it tonight, watching all games and add results in real time, if you absolutely need to know which place does your team ends up.
Because, as you probably know already, it affects how the bracket is made: 9th and 10th would play against 23th and 24th, 11th and 12th would play against 18th and 19th, and so on. Also, finishing between 9 and 16 means playing the second leg of the knockout at home.