Do you have any team mates in Diablo which helps you along the journey?

Answer 1

You can.
You can play it on your own machine. In that mode all you have as a companion is a mercenary that joins you. Starting out as an amazon, then fighter, then mage.

If you go online (which is free) then you also can have other players join you in the game. Its really easy. People pop into my games all the time on the online servers asking to group up because it increases all of the games benefits.