Greetings!

Hello!
This (That) is my first post in (the) notebook!  / in the notebook section!
I want to write here whatever comes to (my) mind, (.) maybe with, or without, errors . I'll wait for your corrections and comments.
Thank you!

Welcome, and well done! Almost error free! I have suggested combining your second and third sentences as the sentence 'maybe with or without errors' follows on naturally from the previous sentence.