Hi guys. Hi guys.

Hi guys! Hi guys!

You can end a greeting like this with an exclamation point or a period. Based on the enthusiasm in your post, I'd suggest an exclamation point. Some English speakers think that "guys" shouldn't be used to address mixed-gender groups. Their argument is that "guys" only refers to men. This might vary by region and age; I'm in my 30s and grew up in the US, and "guys" sounds normal to me. If you want other options, "hi everyone" and "hi folks" are good natural-sounding alternatives.

I'm learning English. I'm learning English.

I'm learning English. I'm learning English.

"I'm" needs an apostrophe because it's a contraction of "I" and "am." "Im" is not an English word, so a typo isn't confusing. However, there are some words that change meaning if there's an apostrophe ("we're" vs "were", "it's" vs "its"), so it's good to get used to the correct spelling.

I really want to be able to speak English like a native . I really want to be able to speak English like a native.

I really want to speak English like a native . I really want to speak English like a native.

I've just found this site. I've just found this site.

I've just found this site. I've just found this site.

This is a valid sentence, but it's an abrupt place to end the post. It's something you would usually say earlier.