Buy the game, download the portable launcher, then run it once to download the game files. Once the game files are downloaded, you can play it offline. Anyway, you can't get Minecraft for free...
Getting onto Minecraft Multiplayer is very simple. All you need to do is when you get onto Minecraft you click "Multiplayer" instead of "Singleplayer", "Mods and Texturepacks" or"Options" and type in...
You can try download minecraft from usenet, but if you try, do not enter any username or password in your downloaded minecraft.exe. To play multiplayer, you have to buy the game.