Your sex is your biological
gender that is assigned at birth. If you are born with a
penis, then your sex would be male, and if you were born with a
vagina, then it would be female. Here’s how it gets complicated. Gender identity and biological sex are two different things, so if the two aligned, then you are cis(gender), however if they don’t, you are trans(gender). So a trans man’s sex would be female, but gender would be male and vice verca for trans women.