I can explain it to you, but you will be like, that sounds stupid!!!
So what I will suggest is get a buddy who has the game and ask him/her to let you play for 30 minutes. If you aren't hooked in 30 mins the probably isn't for you.
Short explanation.
You start the game, you have nothing except the clothes on your back. You are on a world that has been pre-generated and is about 6 times larger (about 30 million miles by 30 million miles) than the Earth.
You see a tree, you punch the tree, you get wood. You take wood, you make wooden planks, you take wooden planks and make a crafting table, you place your craftig table and make sticks from planks. You combine sticks and planks and make an axe, a sword, a pickaxe and a hoe.
You use your basic wooden tools to mine for minerals or other materials to create better tools, stone, iron ,diamond.
You have to build shelter before it gets dark, because at night you will be assaulted by hordes of zombies, skeleton archers, spiders, etc. You play a game of survival in this blocky 3D world where you must fight to survive. The world consists of the Overworld (normal world with dirt and water where you first start), you also get the Nether, a place below the bedrock of the Overworld, a hellish place filled with strange and dangerous creatures and also The End, a place surrounded by the void and darkness with a floating landmass and lots of Endermen and the Boss in the game, the Ender Dragon.
Also the graphics are very basic and pixelated, but if so inclined you can get some HD texture packs by adding some mods to your game - MCPatcher or OptiFine HD3 MT.
You don't have to play the survival aspect of the game, you can use the creative aspect of it as well and take some time to build a full sized replica of the Starship Enterprise or recreate your favourite characters by making pixel art. The game is insanely huge and fun also the game is priced at R220 depending on exchange rate, so not a bad price for a game with endless possibilities.