Ciao Marco, I hope you find my corrections useful, please let me know if you have any questions, I would be happy to help you!

You wrote:

Just arrived here

Hi everybody, i have just joined this group. I am very excited about all the things that i can find here.i have been practicing english for several years but i don t feel i am fluent. I hope this system can allow me to make some progresses. Tomorrow i will have my first official lesson with a teacher. I will let you how it has gone

This entry should be written as follows:

Just Arrived Here (The titles of your note book entries should all begin with a capitol letter)

Hi everybody, I (“I” refers to one’s self and should always be capitalized) have just joined this website. (You could say “group but it would be better to say “site” or “website”) I am very excited about all the things that I (“I” refers to one’s self and should always be capitalized) can find here. I (There should be a space after “here” and then you can start your next sentence) have been practicing English (Proper nouns like “English” should always start with a capitol letter) for several years, (In most but not all cases there should be a comma before a coordinating conjunction) but I (“I” refers to one’s self and should always be capitalized) don’t (Don’t is a contraction of the words “do” and “not” and an apostrophe should be used) feel I (“I” refers to one’s self and should always be capitalized) am fluent. I hope this system can allow me to make some progresses. Tomorrow I (“I” refers to one’s self and should always be capitalized) will have my first official lesson with a teacher. I will let you know (You need to tell the reader what you will tell them so add the word “know” after “you”) how the lesson went. (“It” is too general of a word and should be replaced with “lesson”)

Just arrived here

Hi everybody, i have just joined this group. I am very excited about all the things that i can find here.i have been practicing english for several years but i don t feel i am fluent. I hope this system can allow me to make some progresses. Tomorrow i will have my first official lesson with a teacher. I will let you how it has gone went.

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Benvenuto Marcoavataneo! It seems your English is good, and you have found the right place.
And don't worry, not everyone will go cray with their corrections! lol!