I'm glad to meet you!I hope we can make progress together.

Hello,every one.I'm very excited to join italki.
First, ( ,) I want to thank (thinks) one of my important friends, Mike. He, selflessly/kindly, (His selfless) introduced me to this community. If he hadn't (didn't) told me about this website, maybe I would (i'll) never have known. (about it.) (And) Now, he also helps me to improve my English. (hardly too.)
I really want to improve my English (,) as I make many (have lots of) mistakes in my sentence construction and (,) I would (i'll) be very appreciative if you could correct me. (my mistakes.)
Thought,it's very late in my country,it's 2 am, (.But) I wanted  (write them down) to record in writing the first day I came here. (,and) I look forward to making (make) friends with you (,) and I'll do my best to teach you (your) Chinese.
Good night every one，i have to go to sleep.Have a nice day~

This is a good start and a very informative article. You have a recurring error through this piece which is simple to correct - the word 'I' and short forms of 'I had' and 'I will' (I'd and I'll) are always written with initial capitals. Correct this and you will eliminate about 50% of the grammatical errors.