How to improve my English

I want to make friends with everyone to improve my English, but I don't Know how to make friends. I say "Hello" and then keep silient because I'm too shy.

Actually, I don't Know why American and Englis don't use the simple verbs instead of the complex word, such as why they don't say "It's good for u", but sometimes they say "It will work for you", etc.

Thereforce, I hope some friends can explain it to me.