ok so basically
Discourse is a theory of reality, in a way. in this theory, Discourse is structured by anything that contains meaning - language, imagery, stories, etc. and this Discourse comprises all of how we see things. it’s an active theory, so we CREATE Discourse through social acts like marriage. even talking is an act that creates Discourse. we even create ourselves within Discourse. Discourse is normative - it’s all about social norms, how people act, how we think things should be.
so, say you’re gay. you look to the LGBT+ community, you see all their norms, and you mould yourself to identify with these norms. this is called subjectification.
the fun thing is we THINK we already are these things (male, female, gay, straight, etc), but actually we are MAKING ourselves those things.
then there’s some complex stuff in that Discourse is always related to power. Discourse can shape how we see the world, and can be used to reinforce a certain group’s power. but it can also be used to challenge how we see the world, and challenge power.
the distinction between heterosexuality and homosexuality is largely due to Discourse, and it happened sometime around the 1600s (according to Foucault). before, people just engaged in a variety of sexual practices without those practices categorising part of their identity. but then we started relating sexuality to reproduction, casting out sexuality that wasn’t to do with reproduction, and categorising the norm as heterosexual.
BUT because of this, a resistant Discourse can spring up, to challenge these norms. by saying anything other that het is deviant, the first Discourse created a space for the second, a space for deviants to create their identities, their own Discourse.
advertising is a really good example of how multiple Discourses can exist - there’s loads of Discourses regarding how women are right now. and we can see all of these in adverts. women are weak, and so there are adverts that express that. women are strong and capable, and so there are adverts that express that.
and that’s pretty much the key points. a lot of people like using Discourse as a theory of gender, because it’s not biologically determinate, and everything within Discourse is fluid and creative and social. but Foucault himself kinda played down gender and race, so.
anyway i hope that helps explain it! it certainly helped me revise :)