Three advantages of studying abroad (I'm always confused with the tense...pls help me out)

In my opinion, there are three advantages of studying abroad.

First of all,you can learn more about a new language. Studying abroad forces you to speak a language that you aren't familiar with because it just leaves you surrounded with the foreign circumstances. However, owning a new foreign language skill always winds up making you more competitive in the business market, which means that it makes you remarkable comparing to those who only speak their mother languages.

Secondly, you will become more independent. When staying abroad on your own, you (will) need to approach whatever means can make you survive, and to conquer the physical and mental difficulty to move on. For examples, you may have to learn how to cook, how to pay your rental fee alone, and how to socialize.

The Last but not least, you will widen your horizons. If you have never been to any other countries, you will be constrained to learn more information and to think in an unlimited way. Under such conditions it is detrimental to your future and kills the best person you might be in the future.

Good work!  "Last but not least" is a saying that is basically always used without modifying it, so I wouldn't switch it up. Your word choice with "kills" in the last sentence is a little dramatic, but nonetheless, good work!  When using numbers in this context, you use ordinal numbers, (first, second, third, fourth, fifth, sixth.  The first three are the only ones that have a weird ending, every other one ends in -th.) Also, the saying "widening your horizons" or "they are widening their horizons" is always plural.  It doesn't really have a hard and fast rule.  Great work!

My favorite sport (please correct me if you can)

My favorite sport is soccer, I just love it. I watch every important game on t.v., and I like to see my team winning. I'm a fan of Universidad Catolica Football Club, but I can't remember when I chose to be of that team. I was 5 year old or less, I'm not sure. When I have a game to play and I feel bad or nervous, I just need to stand on the field and my whole system feels already fine, it's a funny thing but I always feel better playing soccer. In Christmastime my dad always gave us a soccer ball, he knew that my brother and I would be very happy with that gift.

Buen trabajo!  A few things: always capitalize "I", and remember the difference between "choose" and "chose".  Chose is always past tense! (http://writingexplained.org/choose-vs-chose-difference).  Also, in the last sentence, I think you should use "I", instead of "me". (http://www.elearnenglishlanguage.com/blog/english-mistakes/i-vs-me/)

English learning in China.

Hi, everyone. What follows is a text written by me. Welcome to correct my mistakes.
Today the number of people learning English in China is increasing rapidly. In fact, China may have the largest number of English learners.  Chinese students have to learn English from the third year of primary school to the second year of university.
But the learning effectiveness is not so good as one might expected. After ten years of learning ,their English becomes deaf-mute English. Many students couldn’t understand what a native English speaker is talking about, and even don’t know how to greet others in English.
One reason is that they study English just in order to pass the exams.They always lose sight of the practical ability of English.  Throughout high school English teaching in China, we can find that a large number of students who get good marks on the entrance examination yet have poor ability to apply it into practice.

Hen hao!  I made a few small edits to either make it sound more natural or to correct grammar if there was a slight error or two.

Please correct my note

I got some mosquito bites on both my legs because I didn't put on a insect repellent spray when I went to a zoo yesterday.
I scratched my legs while I was sleeping. My left thigh is the most itchy because it swells too much.
I put a medical cream on it and I endure.

I speak English natively and am learing arabic. Wa anta min wein?