1. Find it in entities and click the "Fun + Games" category and then spawn it (or spawn it through the dupes tab and then spawn it)

2. Place the Admin Cannon in a position where the Lua Block wont fall out.

3. Insert the Lua Block into the Barrel of the Cannon (also found with the Admin Cannon in entities).

4. Click E on the Car Battery Prop on the back of the Barrel.

It should then fire the Lua Block out of the Admin Cannon.