There is a lot of confusion, and it's all unjustified because the truth is very simple
There are only two sexes. But there are myriad genders. Two often people relate to gender, the same understanding of sex.
Sex is what is given to you at birth based on your genitalia. It's not a matter of debate unless you get a sex-change. At birth, you are either man, woman, or possibly a hermaphrodite. That is indisputable.
But it is not so definite or binary with gender. In the issue of gender it is psychological, not a matter of opinion or 'feelz'. There is very little to dispute. There is not a definitive Man or Woman in the human gender identity. There is a Man and a Woman, but there is a whole spectrum in between where people can identify how they wish. Sex is binary, gender isn't
Source: I am a gender non-conformist in theory