I hope to be corrected by my friends all over the world and I also wish to help others to improve their Vietnamese also (which is my native language).

I have 6 months quite free and, so I'll try my best to learn English

I'm trying to improve my English skills via this website.

* I guess plural, since English skills are many (reading, writing, listening...)

I hope to be corrected by my friends all over the world and I wish to help others to improve their Vietnamese also (which is my native language).

* "my friends all over the world" is grammatically correct but not what an English speaker would say. (You're Welcome!)

I have 6 months quite free and I'll try my best to learn English

I don't know what you mean by this sentence.

Maybe you mean:

"I don't have anything to do for 6 months so I'll try my best to learn English."

I'm trying to improve my English language skills via this website.

Although I have replaced "English skills" with "English language skills", this is just a suggestion. "English skills" is also correct.

I hope to beget corrected by myions from friends all overround the world, and I also wish to help others to improvewith their Vietnamese also (which is my native language).

Remember to use the plural form of 'friend', since you are referring to more than one person.
Singular: 'friend'
Plural: 'friends'

I have 6 months quite free and I'llam quite free for the next 6 months and I'm going to try my best to learn English.

I'm trying to improve my English skills via this website.

I hope to be corrected by my friends all over the world and I wish to also help others to improve their Vietnamese also (which is my native language).

I have 6 months quite freeam quite free for 6 months and I'will try my best to learn English.