What do you need to understand? Gay is being sexually attracted to some one of the same sex and bi just means you're attracted to both genders. It's not a choice but a biological feeling in the brain which hardwires you to fantasize about either gender you're set to be attracted to. I always figured it had to do with some males and females accidentally obtaining qualities of the other gender while in the womb, so you have some guys who are feminine and gals who are masculine and often times attracted to the same sex because they have opposite gender traits. Hey, guys have nipples because we all start out "female" apparently in the womb but once the gender codes kick in, males lose the ability to develop breasts as they age after they're born and hit the puberty period. I hope that answers all of your concerns.