Me too! I am also a free member at chess.com (@datfreshmandude if you're daring to look for me;) ) and Chess Mentor has helped me to a small degree. It has helped me in openings, and the advantage to Chess Mentor over Tactics Trainer is that Chess Mentor not only gives reasoning for why a solution is right/wrong, but it is also written by GMs and IMs (at least I think they are). So you are almost sure to get a good lesson out of the day.
The problem with some of the puzzles (most, I daresay) is that they don't apply in 99.99% of the games you play. Some of them you have to be in that EXACT position to really get anything out of it, in the long term. But it does help you look for things you have never seen before.
For me it has taught me when to make a sacrifice, for example, to sac a rook for a bishop. I never even considered it before, but now I am looking for ways like that to make my position better.
Because of chess mentor I now look for better ways to improve my position. In fact, I would much rather have a good position then be up in material. I had an opponent that was ahead a full rook for 10 moves, but I ended up destroying him because of his weak kingside.
Things like this you'll eventualy catch on.
But if you really want to get better and improve, here's what you do: You lose games.
I'm not recommending this on purpose, but you learn a lot from lost games. You learn what things you should have taken advantage of but decided not to... and also, in my case, it will tell me that I should not have been so recklessly aggressive. (I play aggressively, open position, and love queenside castling in order to full on assault the other players kingside).
If you are a free member on chess.com, which I assume from the information you have given, I recommend playing as many tactics trainer and chess mentor puzzles that it will let you. (normally about 6 total). But best yet is to play against other players.
Dont just play against fellow players who are the same skill level and rating as you. Play against players who are rated much higher. They will teach you a lot when you lose.
Play against lower rated players. they will teach you how to better find holes in their positions because almost all lower rated players have the same Achilles Heel: weak pawn structures.
Good luck and I hope you won't hestitate to contact me if you need any more help or just want to play a game. I like analyzing games with the player afterwards whether I've won or not.