Your writing is perfectly understandable, though if you are aiming for fluency, may I suggest changing "I got the C1 at the..." to "I got my C1 at the..." since the possessive is more correct in this context.

Practice makes perfect, as the saying goes. 

Let's start in here!

This is my first time in this webpage. I don't know how it works but I'll find it out as I get used to it. I've been learning english for a long time, and I got the C1 at the official school of languages, but I really feel that I need to learn more and practice the language with native speakers.

Let's start in here!

This is my first time on this webpage. I don't know how it works but I'll find out as I get used to it. I've been learning English for a long time, and I got my C1 at the official school of languages, but I really feel that I need to learn more and practice the language with native speakers.

Let's start in here!

This is my first time on this webpage. I don't know how it works but I'll find it out as I get used to it. I've been learning English for a long time, and I got obtained the C1 at the official school of languages, but I really feel that I need to learn more and practice the language with native speakers.