Here’s a great video by the YouTuber CGP Grey explaining how first-past-the-post voting system works and some major problems with it. It is kind of sad that the system we use in the U.S. today by nature leads to a two-party system. There is a lot of work that needs to be done in the future looking into the problems of first-past-the-post.
Here is a follow up video explaining an alternative to first-past-the-post.