Which openings to practice as a beginner?

Can you share some ideas which openings to practice as a beginner? 

There is no need to reinvent the wheel.

Chess.com has spent tens of thousands of dollars developing lessons here for beginners that cover these very complex subjects in a way that is time tested and will hopefully sustain your interest.

https://www.chess.com/lessons/guide

Chess Openings Resources for Beginners and Beyond...

https://www.chess.com/blog/RussBell/openings-resources-for-beginners-and-beyond

https://www.chess.com/blog/RussBell

There are quite a few good suggestions on here, and certainly RussBell's guide has been a lifesaver!

It's hard sometimes to understand what an opponent's idea is when they play a move you haven't seen before. When I'm looking through some of your games though (and even the rapid games), a lot of moves are made super quickly with no consideration of what free pieces you can take or if any of their moves attack yours. If the opponent makes an unexpected move, I'd take advice from former world champion Vladimir Kramnik: 

1. Check to see if you have any tactics that immediately win material or the game
2. Check to see if your opponent has any tactics that they're threatening to play
3. What's your opponent's plan with this move? Can you do anything to stop their plan?
4. If there are no tactics, and the opponent doesn't have any clear plan, proceed with yours. 

After looking through your games though, I think that the reason you're starting to be defeated more and more isn't because you're trying to adapt to your opponent's moves. I think it's because of all of the tactics you miss, which in some cases is just pieces of yours or your opponent that are ready to be captured. If you feel like you're missing these moments, it might be helpful to practice your tactics?

If you do want to commit to one or two openings, have a research of the common tactics in that opening, and the different middlegame strategies you can go for. As an example, I play the Caro Kann with black, which you'll see below. In the exchange variation (where the pawns are swapped), I will often try and play for a minority attack. 

Knowing these plans comes with understanding the structures. Get to know yours for your opening and with some practice in tactics, you should be winning more of your games.

Watch a youtube video on the opening you want to play, or on openings in general and then play it.

https://www.chess.com/blog/KeSetoKaiba/opening-principles-again 

When starting out, using chess opening principles is typically more useful than trying to memorize specific opening moves. Your opponent might not play into the exact moves you've memorized, but chess opening principles are usually going to be correct in all openings because their concepts are foundational to the game of chess. By using opening principles, you can reason through your opening moves and maybe even play mainline opening theory without knowing it

@1

"whenever I make a good move it is merely luck."
++ You do not win games by good moves, you lose games by bad moves.
Check your intended move is no bad move.

"learn one or two openings" ++ That will not help you.

"if the opponent makes an unexpected move, my opening plan just collapses." ++ Then think!

"some basic understanding of what am I missing?" ++ Apply opening principles

1. Play your d- and e-pawns only.
2. Play your knights before you play your bishops.
3. Do not move the same piece twice.
4. Do not pin the KB with your QB before the opponent has castled O-O
   
   "What to do when the opponent makes an unexpected move?" ++ Think!
   
   "Am I starting to be defeated whenever I need to start adopting to my opponent's moves even thougt I play with the white pieces?" ++ No. Always adapt to your opponent's moves. You are not even starting to get defeated with black. You start to get defeated when you make a bad move. 

Hi, 

I just wanted to thank everyone who answered, i have the same problem as the person who asked the question and i feel like these answers are going to be very useful !