Main Page Categories

Ok I am quite new to this, but I have it running, so it’s a start. ?? What I wanted to do is only have ONE category show up on the main page. In essence, say the main site only has posts from the GENERAL category. But on the top right, there are additional categories to choose from, and they can load fine.
As it is now all categories show up on the main page when a new post is made… I didn’t know how to specifiy say only one category, or two or whatever..
Thanks!