trans people: What is gender? What makes you a woman or a man? What makes a woman a woman and a man a man?

Gender is male or female. It's determined when you are born by looking at your primary sexual characteristics. Gender and sex is one and the same.

Gender is class. Women are people who have been predominantly perceived as female in their formative years and men are people who have been predominantly perceived as male. Gender identity is something different and appears to be determined by the nature of the corpus striatum.

Gender is a very complicated matter especially thanks to SJW snowflakes. A great majority of the human population still identifies as either male or female therefore there's only 2 genders. Sex and gender have been used interchangeably as synonyms for many years (you especially see this in doctors forms, job applications, or bank forms) through there are some cases where it's more appropriate to use one over the other. Gender expression is closely linked to gender identity. In the case of transmen, they think "I act and dress in a very masculine manner quite often for a girl, maybe I was supposed to be a boy." vice versa for transwomen. I'm not that transphobic anymore, but I still often point out there's many people who act and/or dress like the opposite sex without feeling the need to get a sex (feminine gays, butch/masculine lesbians, tomboys and tomgirls). If you are trans good for you, I'm sure you are a nice person

Have you ever seen the movie "The Matrix"? There is a character named Switch who was played by a very talented actress, Belinda McClory. Her character is biologically male. However, the Matrix is a projection of your residual self image. Inside the Matrix, Switch is a female, thus the codename. This is a great example of what transsexuallity is. Our bodies might be one gender, but inside our minds are another gender.

I'm not trans

"Is gender by itself just a collection of stereotypes of people of that gender"

No. Gender stereotypes are not gender.

"What does identifying as a man or a woman mean? What does being a man or a woman mean?"

Its kind of like just an internal thing. Kind of like sexuality. Its just a thing that you know thats hard wired into our brains. It has nothing to do with gender expression, gender stereotypes or our bodies etc.

Sex is in the brain regardless of outside appearances.

What's in your brain?