You're alright. I've asked the moderators to move it to the general discussion section.
You should copy and paste minitest into the .../minetest/games/ directory and then go to the minetest.exe as Esteban said. At the bottom of the minetest screen, there is a set of icons, one is the minetest logo, another is a green box with arrows, which is minimal, and the other should be Minitest. If you click that logo, then you should be at the minitest menu. Then, make a new world, by pressing new, name it (maybe you are able to define a seed) select v6 as your magpen (v7 isn't done yet) and press ok. Then, launch your world by pressing play. You should be in a singleplayer world. (Make sure creative mode is checked and enable damage is not.)
Minitest is a subgame of Minetest, which itself is an engine. Minetest comes with something called minetest_game (on
http://www.github.com/minetest/minetest_game or bundled with windows), which is a subgame that is meant for default use. Minitest is another subgame, just like minetest_game, but made by a person called PilzAdam. Minitest has different features than minetest_game, as should all subgames. In fact, I have made my own subgame, called Lux_Solis. To put it in a nutshell, a subgame (like Minitest, minetest_game, Lux_Solis, or Carbone) is a set of mods which are used to define the gameplay. But anyway, I hope my explanation helped.
Welcome.