Correction:  Student's sentence   Corrected sentence        Grammar explanation       Better sentence            

Usually, if I do university classes or things that I have to do, I have a little time to get a license for my jobs and I want to do for hobbies.

So When it's vacation, I want to try various hobbies, develop my basic physical strength through exercise that I usually do, ad try hard to get a certificate! 

Usually, if I do university classes or things that I have to do, I have a little time to get a license for my jobs and I want to do for hobbies.

This sentence is correct. 

So when it's vacation, I want to try various hobbies, develop my physical strength through exercise that I usually do, and try hard to get a certificate! 

Capital letters are used in the beginning of the sentence or proper nouns. "When is not a proper noun."

Most of your sentences are correct though I encourage you to make longer sentences next time.