There are lots of great plugins out that extent CMSimple with new functions. The Menumanager
in CMSimple 3.2 SE is a plugin for example.
You can find plugins at cmsimplewiki.com
and the CMSimple Support Forum
To install plugins use the included plugin-manager. Some plugins may not work together with the plugin manager. If that is the case, you can just upload the unzipped files with FTP. Most plugins should work without problems however.