infinite lights are represented by a large white circle with 3 arrows, point lights are small rings, spot lights look like klieg lights (cylinder with flaps). you can make them visible the same way you do other objects -- window -> parameter dials -> properties tab -> visible checkbox. that tab is also where you can change one light type to another one. they get created outside of the standard camera view, so to see them you either have to move them closer to the origin, or pull the camera back far enough. i don't move the dials because they're not precise enough for me; i just type in the values. if you just make an empty scene, create a light, change x, y, and z translate to 0, you should see it sitting right smack at the origin.