Hi Marius, good for you to keep trying. It’s gonna take more than a couple lessons though! Don’t give up. There are a few things we all must do. If you’re starting out follow my free lesson videos which you can link to from the home page.
You need to work on:

blowing / air support
embouchure
fingering exercises (scales & arpeggios are best)

You will see simple but very good exercises like long tones, and doing a simple major scale…just start slow and evenly and play loud. This is the best way to develop your tone.