Thousands of variations on Opening books seems to be so impossible to be memorized by begginners and intermediate players. Even trying to understand the core of each opening line is already an extreme task.

 

What is the best way to learn and understand deeply (or sufficiently) on each book... in order to be able to decide and choose well which line and which variations to follow in the real-life games???

Best way is to play an opening you want to experiment with or research first that feels comfortable to you (1.e4 or 1.d4 for example - which one do you like).  Play the opening with any opponent, write down the moves, then after the game, go over the opening with your reference book or a strong computer or database.  See where you varied from the book and how might you improve.  Study two openings as White and two openings as Black.  Find all the traps and short games (under 20 moves) associated with that opening and study those games.  Soon, you will survive or be better at the opening than your opponent, which should lead to more won games.

Thousands of variations on Opening books seems to be so impossible to be memorized by begginners and intermediate players.

 

Beginners and intermediate players will not reap much benefit from studying opening variations deeply.

 

Even trying to understand the core of each opening line is already an extreme task.

 

For a beginner it's good to know opening principles. Mastering this knowledge is one of the keys to getting much better at chess.

 

For an intermediate player it's good to know a few lines and the main ideas behind them. Eg, in the line 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.a3 Bxb4 the idea is White has lost a tempo and doubled his pawns in exchange for the bishop pair. Playing a few example games shows how to exploit this edge.

 

See where you varied from the book and how might you improve.Find all the traps and short games (under 20 moves) associated with that opening and study those games.

 

This is good advice. I have a small database of all the traps in my opening which I study periodically to make sure I stay sharp.

Play through many master games in the openings you wish to know. Then you will get a feel for where the pieces belong and the typical plans and ideas that the +2200 players come up with.

 

I use www.chesslab.com for my game database, very easy for searching opening positions.

play correspondence chess.

www.redhotpawn.com

 

You're allowed to use books and databases during your games. Play the openings you usually do and when you dont know what to do look up your opening. Best way to learn new variations and get practical experience. 

Thank's for the info I'll try that.