Minecraft Junkie

Of finally downloaded it today.
Last time I played Diablo... well it was the first Diablo.
Before I get in too far. Is there a difference now in this game between single player or multiplayer??
I started single player but I still see people chat in bottom left. Or there is no difference??
Can someone explain it to me and also if anybody already playing together so I can join??
I usually play barbarian

Play with us.. it is all I have been playing for the last week I will help ya out add me as a friend, I am on mumble too

Are there squids in this game?
Haven't checked how much it costs

Whats your user name or do i add you some other way?