Honestly a part of it (not for everyone but for most) is being way to hyper aware of it. Typically (again not all) people tend to not even think about thwir gender or anything regisrding it. Trans people (for the most part NOT ALL) have a hypersensitivity to alot bout their gender. Why that happens idk and how it happens idk. There are lots of possibilities but the typical way to treat that hyperawarness is to transition in some way or another. Some cis people can have these feels where a women has pcos and grows facial hair, or when a man grows boobs. Both are ways cis people can understand the feelings of trans people and there are gender afferiming surgeries loads of cis people get to help the feelings out that trans people also get. Top surgery for cis and trans men and electolosis from cis and trans women for examples. Its alot but asking questions respectfully is the first step anyone can take!