Exterior door knobs come in two different types, and each requires a certain type of installation. If your door is ready for a door knob it will have either a round hole for the door knob or square door prep, and you'll need to choose the right type. Tubular locksets are designed for the round prep, and mortise locksets are designed for the rectangular prep. You can buy different styles of handle and lock options for both of these types.
Knob, Lever or Latch
Exterior door knobs come in three general types. The knob is the standard knob that you turn and it can be round or in a variety of shapes. Levers are handles that you push down and pull up to open the door. And latch door knobs have a stationary handle that you grab and a latch that you push down with your thumb. The style you choose depends on the look you want.
You can choose an exterior door knob that has a deadbolt built in to the top, or you can choose a separate deadbolt assembly. If your door has been pre-drilled, be sure you purchase the correct type for your door.