What do I need to place stepping stones?

I want to put a few in my yard. I had thought that all I would need was the stones and a utility knife. A guy at work said I would need a mattock.
I think that’s a tool which looks like an axe but what the hell do I know? Does anyone have any tips for taking up the sod and laying the stones? Why wouldn’t a utility knife work? It seems like I could just lay a stone down and cut around it, then lift the piece away and stick the stone in.