The basic premise behind the social learning theory is that people learn behaviors from observing the ways that other people act. So, if a child is around parents and role models that constantly yell, then they learn pretty early on that yelling is acceptable, and a way of dealing with problems and stress. That is just one example. Let's take that concept and apply it to gender and homosexuality. Let's say that a little girl is watching her mother get ready for a party; Mom puts on a nice dress, curls her hair, puts on make-up, and sprays on perfume. The next time the little girl is going somewhere, she mimics all of the things that her mother did; she puts on fake make-up, sprays fake perfume. She has learned a female gender role from observing her mother.
If a child is around role models that are homosexual, they will probably pick up behaviors and traits exemplified by those role models. If they grow up surrounded by only women, it could be that they find it easier to relate to or be around women. The same applies for men.
Another angle to this perspective is that some people feel that social learning is highly responsible for girls behaving like girls, and boys behaving like boys. If you take a girl and constantly model classically male behaviors (like playing contact sports or using power tools) then that girl might behave more like a boy than a girl. The modeling is the key to social learning theory; people learn what is being modeled around them, and that applies to gender roles, and to homosexuality. I hope that those thoughts help to get you started, and I also provided some links below that might be useful. Good luck!