Sexual capital is about how having certain qualities makes you attractive to other people. It is something like social "currency", or points that you can use with others to get attention, or even get ahead. For example, if you are good looking, popular, or have a lot of money, you have a lot of sexual capital, which means other people find you very attractive. They may want to be friends with you, date you, or even get help in some way from you. In other words, having sexual capital can help you get ahead in life.