Let's begin with a breif description of what Yaoi, Shounen Ai, Yuri, and Shoujou Ai is.
Yaoi: Although some people have more in-depth and opinionated views on what the word 'yaoi' means and where it comes from, most people will find it easier to describe it as a male x male relationship. Unlike shounen ai, yaoi is usually more sexual and mature.
Shounen ai: Shounen ai is sometimes considered a synonym of yaoi, but in actuality, it's a bit different. Like yaoi, shounen ai relationships deal with two males, although the relationship is not as sexual as a yaoi relationship.
Yuri: Yuri is basically the female counterpart to yaoi. A sexual female x female relationship.
Shoujo ai: Shoujo ai has a much deeper meaning than shounen ai does, but to save everyone time and unnecessary confusion, I'm going to go by a more popular/recent definition. Using fan-based terms, shoujo ai is a non-sexual female x female relationship.
Remember, by entering this subforum, you're allowing yourself to be exposed to male x male and female x female sexual relationships. If this makes you uncomfortable, this isn't the place for you!