Usually you use one hand to hold the screw or nail until it penetrates and is held in place by the wood.  But singlehanded I use a magnetized screw driver and/or screw bit for hanging drywall in my kitchen.

photo of screwdriver with magnet attached

For the few nails I convinced my wife to hold them in place while I carefully set them.  When I'm by myself I use an old ice pick to make a big enough hole in the wood or drywall so that the nail or screw can be set by hand. It doesn't take much for soft wood but sometimes I have to drag out the drill and bits.

photo of ice pick in drywall then screw/nail in hole