Gymnastics

I practiced gymnastics on gym today too.  -- I practiced gymnastics at the gym today.  (You would say "too" only if you had said you did something else before)
Today come other junior high school.  -- Another junior high school came to visit today. Or..... came to train at our gym today, too. 
They are very weel. -- not sure what word you mean for "weel"
They are ten about. --  There were around 10 of them. (Or if you mean their age is 10 --  They were about 10 years old, on average.)
They practice many technique. -- They practiced several different techniques.  
I had a very good time at the practice time.  -- I had a very good time at practice today.