I'm sure other people in this thread have done a great job talking about the mainstream stuff, so I'm gonna get weird.
Nonbinary identities aren't all combinations of male and female gender traits. There are also nonbinary genders. They're called xenogenders. And nonbinary identities can be any combination of male, and/or female, and/or any number of xenogenders. Xenogenders have traits that you may not typically believe are gendered, or that take the stuff you know in unexpected directions. But what are you expecting from a gender that isn't like anything you know? It's gonna seem weird.
Xenogenders are common among otherkin and alterhumans. Otherkin are people who don't identify as human. They may identify as a real animal, or a mythical or fictional creature, which may be sapient or nonsapient, though nearly all otherkin are themselves sapient. Alterhuman is a broader category that also includes people who only identify partially as human or nonhuman. Perhaps someone who remembers a past life as a wolf, for example.
Sometimes a brain contains more than one person. The brain contains a mechanism for creating a person, an identity, a consciousness, and usually it uses that mechanism once. Sometimes it's used more than once. It's called plurality. Plurality can be the result of traumatic mental disorder, but it can also be healthy.
If I'm an experienced D&D player, will I need to worry about knowing how to build a class? I didn't have any problems understanding KOTOR's character creation, and I actually prefer Mass Effect 1's combat and levelling over 2. I love crpgs.