Hi hon, welcome!
It's a confusing space to be sure, but in the main, it's all about finding folk who feel the same way about gender as we do... loosely based on three key concepts - how strongly we feel we have gender, how rigid our sense of gender is, and how we align against the gender binary...
This gets broken down a little by bi gender (periods of feeling like one gender, more than the other), gender queer - where our sense of gender isn't aligned with our expected gender, but either flows, or is fragmented across our selves - a catch all umbrella for those that don't quite fit into just one space...
So, it's complicated, but a useful way of trying to find our tribe.
Hopefully that made some sense
Rowan