Um I'm bisexual and stuff and I haven't ever head of polysexuality until today, can you explain it please?

In short, it is the attraction to more than one, but not necessarily all [though it could be all] genders or sexes!

If, say, you were attracted to androgynous people and females, you could be polysexual. 

The phrase “polysexual’ arose to classify people who are attracted to more than one gender/sex BUT either do not wish to label themselves bisexual/pansexual OR are not attracted to their own gender/sex. 

I, personally, am an agender person with a vagina. I label myself polysexual because while I can be attracted to all genders it’s substantially less for me to be attracted to female-identifying (cis or trans) people, so I feel more comfortable calling myself polysexual.