Open the Lua Script Library through
Prepare > 
Run Lua Script. Use the appearing dialog to load, save, and execute Lua scripts as well as to create new ones.
For editing, importing, and checking for syntax, Netfabb brings its own editing dialog.
The variable tray is predefined with the current build room to allow direct and quick access to all meshes currently loaded.
Example Scripts
Netfabb comes with a selection of example scripts loaded into the built-in Lua Script Library. These cannot be edited, but you can create copies of them and edit the copies.
More example scripts can be found in the Netfabb installation folder, sorted into Examples\LUA Scripts.