The Silva Compass is the compass Roland Deschain receives from the Old Diseased Man in
The Old Diseased Man handing the compass to Roland Deschain
The Journey Begins. The man wants Roland to bring the compass to the Man Jesus. The compass is pretty much useless to Roland because as he says later in the novels, "One days north is north and the next it could be north east".
In The Man in Black (Comics), Roland gives Jake Chambers the Silva Compass when the two part ways before Roland comes to save him.