handmirror is a plugin for tinyMCE that enables the use of CodeMirror-UI for souce code editing.
To use handmirror you will want to drop the root handmirror directory into your tiny_mce_xxx/plugins directory.
You'll want things to look like this:
tiny_mce_xxx/plugins/handmirror/editor_plugin.js tiny_mce_xxx/plugins/handmirror/dialog.htm etc...
Then in your tinyMCE init call you'll need to add it to the plugins.
plugins : "handmirror,spellchecker,etc..."
And make suer that you add the button to one of the toolbars
theme_advanced_buttons1 : "handmirror,bold,italic,etc..."