How to analyse your games

Start with the opening. If you had a point in the opening where you didn't know what to do, then you need to find out what to do for the next time it appears (which it will). 

Continue on to where the middlegame begins. Ask yourself if you were able to find a correct plan. If you weren't, then you probably don't understand the positions arising out of your opening, and you should look at high-level games to see how they handled the position. 

If you randomly blundered (which is common at lower levels), then you should work on tactics so that you won't do so anymore. You should also try to figure out why you blundered (did you miss some tactical trick, or were you just focused on some other part of the board, etc.) so you can work on that specifically. 

Thank you for the insight. So I should use engine only to seek for tactics, and otherwise look at the game and ask myself if I know what I wanted to achieve at any exact moment?

Do annotations. Make sure there's a reason for every move you play. Even if you use an engine, look at the lines it suggests not just the evaluation number.