You should get the admission letter of the university and go to Chinese Embassy in your country to handle X visa. Beisdes, you need to bring your passport (still valid in more than 6 months), medical exam paper. Apply for the via about one months before you are leaving for China. You have to handle the residence register within 30 days after you arrive China. When you apply for the visa, the officer will decide period of validity, stay and times or entries according to your situation.