
Can someone tell me what does doujinshi mean and what difference with yaoi?

You said, and I quote, doujinshi is "when creators make a manga that's based on established characters from anime/mangas." Which is not always the case, as that is not the inherent definition of doujinshi, though as you said, there are many fanfic doujins.
(Also just realized the way I talk might seem aggressive, I'm really just making a correction)
he is small waist pretty face with a big bang