Posts versus Pages?

I’m sure this is somewhere. If someone could just show me the link, I’d appreciate it. I have to teach a class in ten minutes, so I don’t have time to search right now, but I would like to get this thing working properly…

When I create a “post”, it shows on my front page. But, when someone clicks on the link, it says “Page Not Found”. When I take the same post and copy and paste it into a page, it shows up under pages, and works just fine.

http://www.errantconvergence.com

I am confused about how this works. I’m missing something, probably something simple. If anyone can help me, I would appreciate it!