How do we get a Minecraft account?
If you do not yet have a Minecraft PC game account you can buy it at http://minecraft.net
This button takes you to the page to create a Mojang account, Mojang makes Minecraft and other games.
The Mojang account is what is used to sign in to Minecraft the game as well, so the students will need to know the email address used and the password. (Some older accounts only need the minecraft character name instead of the email).
This page allows you to enter your credit card information to either pay for a minecraft PC account or purchase a gift code to give to someone. The box for the Minecraft name is where you put in the name you would like in Minecraft. This name appears above your head in multi-player worlds. From here you could also redeem a gift code if someone gave you Minecraft as a gift or if you purchased a Minecraft gift card from a brick and mortar store. With a gift card you don't need any creditcard information.
After you hit PURCHASE or REDEEM, you are taken to the Minecraft download sight. Note: it is possible to download Minecraft before purchasing, but it will only work in demo mode for a limited number of hours. Demo mode can be fun for exploring the game, but it is limited to playing alone on the computer you installed it on.
If you have already purchased Minecraft:
If you have already purchased Minecraft of some type you can log in to your Mojang account and see the different versions you may have purchased. Minecraft does make several version. The iPad and Android mobile edition (Minecraft PE), a game console edition for Playstation and Xbox, and a PC version (for MAC and Windows and Linux). Each of these different versions can't play with other versions because they run on different platforms.
The class will be playing on a multi-player server so each student will need a unique game account. The servers don't allow an account to login more than once because it then can't keep track of what they are doing in the game.
This link helps to explain the different types of minecraft accounts. Migrated, mojang accounts, and demo accounts.