It only has the neccessary files to display it properly in the main menu and that’s it. So only metadata but no actual data.

Empty is aimed at experienced Minetest users and modders. At the very least, you should understand the concept of mods, worlds and how to activate and deactivate mods from the main menu.
Although there is nothing in it, Empty is actually a very powerful tool. Empty can be used to activate and deactivate mods easily in the mainmenu without bothering about possible collisions from the game mods. Since Empty is empty, there will never be any collision with it. You can use Empty to basically click your own pseudo-game together or check quickly check how a set of mods works together.
Personally, I have used Empty serveral times for testing a bunch of mods, quite successfully.
Empty itself is of course completely unplayable.
When you start an Empty world as such, you will spawn in a world full of air and the console is flooded with error messages about missing textures.
You also should have stockpiled a collection of mods so that Empty can be of any use for you. Note that mods depending on mods from other games won't work in Empty, i.e. mods with a mandatory dependency on default from Minetest Game. But if you want to test mods written for Minetest Game, you should probably play Minetest Game. ;-)
- Name: Empty
- Tested for: Minetest 0.4.11
- Current version: 1
- Mods: none
- License of Empty: WTFPL