How to Learn Openings?

Hi all:

I wanted to inform you that there is a chess site known as chessable.com, memchess.com, and the program Chess Position Trainer. What I don't like about all these is that they force you to memorize the lines when you are learning openings. Are these websites and program good to learn openings?

Does anybody have any ideas on how to improve these to incorporate the understanding part into chess openings? Personally, I wanted to somehow incorporate the rule out method in chess for candidate moves into one of these, since this currently isn't included anywhere.

Maybe chess.com can make a different chess opening trainer with the following: 
1. what is in your repertoire that you would play
2. what the opening database says
3. what the engine says
So first you would have to play what is in your opening repertoire continuously through the training. If that is incorrect but you still play a playable move that is in the opening database or what the engine says then it will count that as a good move. Then you will be forced to retry to play what is in your repertoire if you played a good move that isn't in your repertoire.

I use Chess Opening Wizard.

Learn piece placement.

Learn Pawn Structure.

FCO or MCO is a very good Openings Manual for non masters.

In a 2006 GM John Nunn book, in connection with opening study, it is stated that, if a "book contains illustrative games, it is worth playing these over first", and the reader was also advised, "To begin with, only study the main lines - that will cope with 90% of your games, and you can easily fill in the unusual lines later."
"... I feel that the main reasons to buy an opening book are to give a good overview of the opening, and to explain general plans and ideas. ..." - GM John Nunn (2006)
In one of his books about an opening, GM Nigel Davies wrote (2005), "The way I suggest you study this book is to play through the main games once, relatively quickly, and then start playing the variation in actual games. Playing an opening in real games is of vital importance - without this kind of live practice it is impossible to get a 'feel' for the kind of game it leads to. There is time enough later for involvement with the details, after playing your games it is good to look up the line."
https://www.chess.com/article/view/3-ways-to-learn-new-openings

"... For new players, I cannot recommend books that use [an encyclopedic] type of presentation [of opening theory], because the explanatory prose that elaborates typical plans and ideas is usually absent, thus leaving the student without any clear idea why certain moves are played or even preferred over other apparently equivalent moves. ..." - FM Carsten Hansen (2010)

"... [Modern Chess Openings (15th ed.)] pretends to be everything for everybody, but it isn’t; it pretends to be up-to-date and relevant in all chapters, but it isn’t; it should be a good book, but it isn’t. ..." - FM Carsten Hansen (2008)

https://web.archive.org/web/20140626165820/http://www.chesscafe.com/text/hansen110.pdf

"... [Fundamental Chess Openings] is not particularly suited for players who are just starting out. I would imagine players rated at least 1400-1500 would get the most benefit from this volume. ..." - FM Carsten Hansen (2010)

https://web.archive.org/web/20140626173432/http://www.chesscafe.com/text/hansen128.pdf

http://www.gambitbooks.com/pdfs/FCO_Fundamental_Chess_Openings.pdf

Before you train openings you have to study pawn structure chess.  Also in addition to the book you should look into the pawn structure 101 series made by IM Daniel Rencsh that you can find easily via the chess.com search tool.

I learn to play openings this way:

• Look up master games in which the person initiating the opening wins (e.g games in which Karpov plays his own variation of the Caro-Kann) and learn from them
• Look up variations that may come up in my games that don't show up much
• Use your opening principles to fill in the gaps
• Analyze my games (usually with the computer) after I've played them
• Quick overview videos on openings (especially the ones from Chess.com

However, be warned - there is sometimes "common knowledge" you may not really understand the importance of for some openings e.g the dark-squared bishop and how Black sometimes sacrifices the exchange to keep it.

I find chessable to be very useful. Chess opening explorer is similar. 

Chess opening explorer costs money one time, chessable is free (but there are paid repertoires/monthly subscription for extra features).