How can I get better at chess?

Possibly of interest:

https://www.chess.com/article/view/can-anyone-be-an-im-or-gm

What It Takes to Become a Chess Master by Andrew Soltis

https://web.archive.org/web/20140708093409/http://www.chesscafe.com/text/review857.pdf

Reaching the Top?! by Peter Kurzdorfer

http://www.thechessmind.net/blog/2015/11/16/book-notice-kurzdorfers-reaching-the-top.html

https://www.chess.com/article/view/don-t-worry-about-your-rating

Simple Attacking Plans by Fred Wilson (2012)

https://web.archive.org/web/20140708090402/http://www.chesscafe.com/text/review874.pdf

https://www.newinchess.com/Shop/Images/Pdfs/7192.pdf

Logical Chess: Move by Move by Irving Chernev (1957)

https://web.archive.org/web/20140708104437/http://www.chesscafe.com/text/logichess.pdf

The Most Instructive Games of Chess Ever Played by Irving Chernev (1965)

https://chessbookreviews.wordpress.com/tag/most-instructive-games-of-chess-ever-played/

Winning Chess by Irving Chernev and Fred Reinfeld (1949)

https://web.archive.org/web/20140708093415/http://www.chesscafe.com/text/review919.pdf

Discovering Chess Openings by GM John Emms (2006)

https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf

Openings for Amateurs by Pete Tamburro (2014)

http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html

Chess Endgames for Kids by Karsten Müller (2015)

https://chessbookreviews.wordpress.com/tag/chess-endgames-for-kids/

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

A Guide to Chess Improvement by Dan Heisman (2010)

https://web.archive.org/web/20140708105628/http://www.chesscafe.com/text/review781.pdf

what's a good modern endgame book?

I hear good things about Shereshevsky's book. 

https://www.amazon.com/Endgame-Strategy-Everyman-Mikhail-Shereshevsky/dp/1857440633

I also heard about Averbach but I'm not sure what book they talk about.

Various possibilities discussed at:

http://theweekinchess.com/john-watson-reviews/endings-endings-endings

http://theweekinchess.com/john-watson-reviews/the-end-game-comes-before-we-know-it

http://theweekinchess.com/john-watson-reviews/theres-an-end-to-it-all

https://web.archive.org/web/20140708105702/http://www.chesscafe.com/text/review645.pdf

https://web.archive.org/web/20140708234309/http://www.chesscafe.com/text/review704.pdf

https://chessbookreviews.wordpress.com/tag/chess-endgames-for-kids/

Before buying any particular book, I suggest going to the publisher's site to see if it is possible to view a sample. For someone with an active interest in beginning to learn about endgames, my best guess is that Silman's Complete Endgame Course is an appropriate choice. Chess Endings Essential Knowledge is one of a number of other possibilities. My understanding is that Sherevsky's book assumes that the reader already has some endgame knowledge and sets out to build on that knowledge. ("... one will not learn the basics from this book at all ..." - IM John Watson)

 The best way to get better at chess is going to a club and getting a coach. I don't know if you have a chess club where you live. it's difficult to make progress without that. If you aren't able to get a coach, you shouldn't read books, but get Chessbase and Chessbase DVDs. There are DVDs for almost everything in different languages where the coaches explain very well. Also, you can find chess videos in YouTube

There are only three books that I would recommend you:

-Silmans Complete Endgame Course - Jeremy Silman

-The Amateur's mind - Jeremy Silman

-Dvoretsky's Endgame Manual - Mark Dvoretsky

What exactly you need and what you should practice, I can't tell you. it really depends on how you play. You should try improve your weaknesses and build on your strenght.