Corrections in red.  Stylisticis in blue.

Just My Thoughts.

Hello, everybody! Nice to meet you if you are reading my note right now.
I am a student in the tenth grade of school. But I really don't know what to be in the future.  It is such a difficult question. I cannot understand who I am and why I live on the Earth. For what reason? Anyway, I do have some purpose.
Certainly, I have a dream. I want to travel around the world, develop myself, my mind, see a lot of cultures, countries, peoples, understand their views of the world, and more...
And to make this dream come true, I have to work on myself all the time. Sometimes I may fall down, but I mustn't give up.  I must fight for my future, for my dream, and try again and again. It is not so easy, but my  dream is worth the effort. 
Thanks for your attention.

Excellently written.  Bravo!