what should I learn

Here is a guide of sorts, you can use:

https://www.chess.com/blog/nklristic/the-beginners-tale-first-steps-to-chess-improvement

By the way, if you wish to improve, playing bullet is not the right thing to do. The longer games, the better for you.

Fast games are fun but to improve you should play longer games. At least G30. It will give you more time to think, check for blunders, etc. The improvements from long games will eventually trickle down into your blitz.

Improving Your Chess - Resources for Beginners and Beyond...

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

Spend time looking at the board looking at what pieces can just be taken for free. Hanging pieces is a major factor at this level. This will require you to slow down and take more time on your moves. Look over your games afterwards for these kinds of things, especially close games or games you've lost. It's not a bad idea to make notes about your thoughts on your moves while reviewing the games. You can post such things on the forums for review, as well as check the chess.com analysis feature, where you can skim through some suggested lines, (focus on the number of moves out that make sense to your position, such as the immediate attack or predicted recaptures, etc. once they start making moves for new plans it begins to be less valuable for this purpose as you might not follow what they are even doing). I just checked over a few of your losses to display some examples so you can see some direct ties to your own games though I point out a few other tactics that popped up. Tactics in general are very valuable to understand. 

ola boa tarde