what do I need in order to get the visa? it is possible to stay there for a month?

Chloe, you should ask your BF to send you an invitation letter together with the copies of his passport information page and resident permit. Then you use these two documents together with your passport, application form and a recent passport photo to apply for a L type from the consular department of Chinese embassy in your country.

If you come for the first time, then you need to provide financial proofs, recent six months bank statement for example. If you don't, your BF should write a letter to explain that he will burden all your cost during your stay in PRC.