A deadbolt is a major security upgrade over a simple latch, and installing one is a manageable DIY job. If you're replacing an existing deadbolt it's quick; adding a new one means boring two holes accurately.
Replacing an existing deadbolt
Unscrew and remove the old deadbolt and bolt mechanism, then fit the new one into the existing holes, connect the inside and outside halves, and screw it together. Most retrofit deadbolts use standard hole sizes, so it drops right in.
Installing a new deadbolt
New installs need a large hole through the door face and a smaller one through the edge for the bolt, drilled square using the template that comes with the lock. A hole saw and spade bit do the job. Mortise the faceplate flush so the bolt extends freely.
Reinforce for security
A deadbolt is only as strong as its strike plate. Replace the short screws with 75 mm (3-inch) screws that reach into the door framing, not just the jamb, and use a reinforced strike plate. This is what actually resists a kick-in.