As the guys said, you'll have an x,y,z and a axis. Best bet is to do all the roughing in 3 axis mode and just index 90 degrees each time, then do your finishing in 4 axis mode to optimise the surface finish. Solidcam has some nice features where you can finish parallel to a curve or to an axis or you can let your toolpath morph from the shape that defines one side of a face to that or the other. So if one end of the face was an arc and the other a straight line, your toolpath woud start as an arc and gradually change as it machines the face to straight lines. Nifty stuff.
Noel.