My new post doesn’t show up on main page…

I just created a new post under 2.5.1. The new post doesn’t appear on the main page, but only appears under the categories I assigned to it. I’ve been using wordpress for almost two years now, and I think I know the basics. This seems like something basic; yet, how do I get my post to appear on the main page like it’s supposed to?

Yes, the post is published, etc.

Thanks!!!