Seeing as this prompt relies on the readings used in your class, it's going to be difficult to help you without additional guidance - what specifically confuses you? Having targeted questions will help you get the answers than can guide you to understanding this topic.
The info that I can confidently provide based on your question is the basic difference between sex and gender. Sex is the body an individual has - usually male or female, occasionally intersex. Gender is based on the social construct of the roles traditionally occupied by male- and female-bodied individuals. Gender and sex most often go together (male-bodied individuals who identify as men, female-bodied individuals who identify as women), but this is not always the case. Transgender people identify with the gender that does not "match" the sex they were born with. Additionally, some people (many psychologists and sociologists) reject the notion of a "gender binary" - the idea that there are two distinct genders - in favor of a gender spectrum, where people don't fit into one of two boxes, but exist on a spectrum of masculinity and femininity.
I hope I was helpful, and please let me know if you have any more specific questions about the topic or writing your response.