Hello!

Hi, my name is Jun Ho Cha.
I live in Sejong.
I'm 17 years old.
My hobby is play playing games.
Please give me advice on my english
I would change this to something like "Please help me improve my English." or "Please assist me on my ability to speak English."

Thank you^^

Overall, your English isn't bad. There are times when it'd be better to connect your sentences and make more complex sentences but aside from that you only had some mistakes. By sure to capitalize the beginning of your sentences and names (such as your name and the names of specific places like Sejong).

Good job! Keep going~