sexual preferences

DS
I do not mean this to be offensive in the least bit, but I saw someone post about a sexual preference I'd never heard of, so I looked it up. Upon looking it up I got curious and googled how many different sexualities there are..... there's a lot. But here is my question there are so many that I feel like are exactly the same just given a different name and the definition worded differently. 
 
Fluid vs. panssexual?
Pansexual vs. bi sexual?
Genderqueer vs. gender fluid?
There are more i could compare... 
  
 Also I don't understand cisgender... it says when your gender and sex align with your biology at birth. So why classify that as something different? Again I don't know how to word this without sounding rude and I'm not trying to. I'm really just trying to understand.