What is it?
NShakedown is a tool to help you organise your user interface. When using many addons, you get a lot of elements appearing over your display such as combat text, spell trackers, raid warnings, casting bars etc.
NShakedown allows you to display and arrange these around each other, so that they don't overlap.
To start shaking down, click on the maracas on the minimap or FuBar, and click again to stop shaking down.
You can turn individual addon shakedown on and off via the menu.
Set a keybinding (I use Shift-Ctrl-S) to toggle shaking, via the standard keybindings menu.
You can access the (Rock) configuration menu by right clicking on the FuBar/minimap icon or using one of the slash commands: /nsd /nshakedown /shakedown