Я думаю, я бы изменить его к этому:

Hello. I am a student in gymnasium, in class 9. I can play the piano and study the guitar, (concern with dance... I don't know what you mean. Sorry!). I am also in a military club. 

I study English, because I like this language, and I want get acquainted and communicate with people from an English speaking country. Maybe I'll go there.

Does that make sense? Good Luck!

Richard

First notebook entry: Introducing myself

Hello. I am a student in gymnasium1 in 9 class. I can play the piano and is study play learning how to play the guitar, concern with and how to dance. Also I to be in to join a military club2.
I study English, because I like this language.   and I want get acquainted  to make friends with people from English speaking countries so that I can communicate with them in English.and communicate with people from Englishspeaking country. Maybe, go there. as I would like to visit these countries.

1.  In English speaking countries, a gynasium or gym is a place where people go and exercise to build themselves up or to lose fat.  It is not a school.  So you need to explain which year of the school you are in so that the correct term can be used, eg, junior high, high school, college etc.  If you don't want to give out such information, just simply write, "I am a student'

2.  Remember you writing is seen by the world and people from other countries might now know what you are talking about.  So what is a military club?  We in the US do not know what it is.  You need to explain.

First notebook entry: Introducing myself

Hello. I am a student in gymnasium, in  class 9. I can play the piano and study play the guitar,  dancing. Also I to be in military club.
I study English, because I like this lenguage and I want get acquainted and communicate with people from Englishspeaking country. Maybe, I'll go there.

First notebook entry: Introducing myself

Hello. I am a student in gymnasium in 9 class. I can play the piano and study play the guitar, concern with dance. Also I to be in military club.
I study English, because I like this language and I want get acquainted and communicate with people from Englishspeaking country. Maybe,  I go there.