My first italki

Hi, mates. Im Moto from Japan and I live in Australia.
I just started using this web site to improve my English skill. I have a native friend who gives me a hand to do it, but I think I need more practice so he introduced me to this web site. I would like to meet people who can brush up skills off each other :)
I can teach you Japanese grammar, vocabulary, idioms etc. because it is my major at university.
I appreciate it if you are interested in me. Thank you.

'web site' or 'website' there is not much difference that I know of.

Nice job :]
You are very good at English.

Corrections (In order):

1 - 'and' joins 2 sentences together so it is good to state who you are talking about again.
2 - 'web site' could be talking about any website, this states it is the current one you are on or contextually speaking about.
3 - 'so' joins 2 sentences. I did this as the second sentence continued the main point of the previous sentence.
4 - You were introduced to the website as websites cannot be introduced to people.
5 - Spelling mistake (everyone makes them)
6 - 'etc.' is short for 'etcetera' so the period shows it is shortened.

Hopefully my corrections are not confusing and that I was able to help.
がんばって！