What are tow hooks and D-ring shackles and where do they install? 

Tow hooks and D-ring shackles allow you to tow or be towed by other vehicles.  You can attach tow straps or recovery straps to the tow hooks of two vehicles and use one to tow the other, or you can use D-shaped metal rings, which can be attached to the D-ring shackles with a bolt.  Tow hooks and D-ring shackles can be mounted to the underside of the frame at both the front and rear of the vehicle.  They are constructed of sturdy steel to withstand the forces of towing. 

Why might I want to install tow hooks and D-ring shackles? 

Tow hooks and D-ring shackles can be very useful for off-roaders.  If one vehicle in your group gets bogged down in the mud, you can run tow straps or recovery straps from one vehicle to another and pull it out.  The tow hooks and D-ring shackles provide mounting points for the straps. 

Can I install tow hooks and D-ring shackles myself?

The difficulty of installing tow hooks and D-ring shackles will depend on your vehicle.  You may be able to mount them to the frame with your bumper bolts.  In some cases, though, you may have to drill into the frame.  You may also need to remove the bumper cover to access the mounting points.