Gender fluidity confusion???

So this is my opinion of gender, and I wanted to post this here because i can ask questions without people getting offended (which is why this is anon.). I just don't understand...
I get that someone can be lesbian or gay (not bi because I feel like you prefer one). I can understand sexuality. I can even understood trans people as long as they totally switch male to female or female to male. Women don't have huge beards... I do not understand how someone can be gender fluid, cisgender whatever. Like what the hell is that? Even if you aren't quite sure, you dress more or look more like male or female, so that's what you are. Like just decide. It's so attention seeking and idk. Like you have male or female pronouns, "they" is plural.. you're not two people. I looked at an article about the different kinds of gender and like half of them are saying you're in between. What do you mean? You're more like one than the other. I don't understand how someone can not lean towards a gender