hHello. Hello.

Welcome! Just correcting your capitalization, which isn't strictly necessary for an online forum like this.

itThis is my first passage ion this platform. This is my first passage on this platform.

I would specify "this" rather than use the more general "it" in this case. Prepositions are tricky in every language. We say "on this platform," though I don't think there's a strict rule to explain why.

I want to improve my English . I want to improve my English.

fFirstly what must I do? Firstly what must I do?

This might sound more natural as "What should I do first?"