Rather than give you a rundown of what Frances McDormand said during her speech, we're going to give you a quick rundown of what an inclusion rider is - because it's what she said at the very end of her speech.
An inclusion rider is something that can be inserted into an actor's contract that requires producers, directors and studios to meet certain standards in diversity, whether it be hiring more women, more people of colour or more LGBT people. The idea was first posited during a Ted Talk in 2016 by Stacy Smith of the Annenberg Inclusion Initiative at the University of Southern California, who studied the data of films released and found - well, what we already know - that casting in films isn't representative of populations generally.
In her Ted Talk, Smith said that it could be argued "only 8 to 10 of those characters are actually relevant to the story. The remaining 30 or so roles, there’s no reason why those minor roles can’t match or reflect the demography of where the story is taking place. An equity rider by an A-lister in their contract can stipulate that those roles reflect the world in which we actually live."
Here's a link to that Ted Talk, and here's Frances McDormand's speech in full.