Here's a fast introduction to OpenEMR, how it works and what it can do. This is a fairly complete set of screenshots taken from a Virtual Machine installation of Linux and OpenEMR (see the Try OpenEMR Today section of this site for more about that).
We suggest that you review these documents in order. They include the screenshots with narratives. The first one doesn't have much to do with OpenEMR per se and so you can skip it if you don't care what's under the hood.