Hello! In my case, I want the Chinese visa for visiting my boyfriend there.

Steffany, you can apply for a tourist L type to visit him. You need to provide those documents: your passport and copy of its data page, the filled-out application form attached with a passport-style photo, and an invitation letter from your boyfriend.
You should pay it at the consulate general of PRC.

And about the letter, how should it be? I mean, is it supposed to be in Mandarin language or in English language? and is he supposed to send the letter to the Embassy, here in Chicago, or I can print the letter from my e-mail?
I will be there only one week. In the page says I have to copy my flights schedule but I do not have that because I am not sure if I could get the visa. What do I have to do about that?
Thanks for answering.

Steffany, it can be written either in Mandarin or in English.
You can provide the fax, e-mailed or scanned copy of the invitation letter if the original one is not required. If possible, you can ask him to send you copy of his Chinese ID card, too.
If you can provide the invitation letter, the round trip air tickets are not necessary then.