To get the game, go to
minecraft.net and make an account. Then make your account premium for $26, download the game, open it, sign in with your account info and hit play. You'll then see a screen that says Singleplayer, Multiplayer, Options and Quit Game. Click on Multiplayer, then click Add Server (at the bottom). Enter Opticraft into the server name bar and smp.opticraft.net into the Server Address Bar. Click done, then double click the icon at the top of the screen.
I hope this answers your question.
