I take a look at your profile and you are solving tactics problems, which is good. So what must be the problem? You should also study endgames and strategy. Avoid bullet. Improvement can also take time.
How can I improve my chess?

Not the openings themselves, but the ideas behind the openings. Memorizing openings at your level is not a good idea. If your opponent make some move out of the book, you will be lost. Better to understand the first moves other than memorizing them. Good luck! :-)

That's a difficult question for me to answer. One thing I can say to you is that when I began to learn chess, I bought about 3 books on openings, and soon they became boring, and I left them on the shelf for long time. Took me some time to understand that those books where good for experienced players, not for beginners like myself. I think that in the day that you will be able to understand every single move at an opening, that's the time to study them. Not memorize, but to understand the moves and to avoid the traps.

Just one more thing, I am talking about long games, OTB or online daily games. I don't like blitz or bullet games.
Possibly helpful:
Simple Attacking Plans by Fred Wilson (2012)
https://web.archive.org/web/20140708090402/http://www.chesscafe.com/text/review874.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/
A Guide to Chess Improvement by Dan Heisman (2010)
https://web.archive.org/web/20140708105628/http://www.chesscafe.com/text/review781.pdf
Here is a good opening guide for you.
https://www.chess.com/article/view/the-principles-of-the-opening
https://www.chess.com/forum/search?keyword=How+can+I+improve+my+chess