How difficult a job it will be is highly dependent on which rails and installation kit you buy. The "universal" kits will require that you drill some large holes into the truck frame rails. You probably want to avoid that. The "custom" kits will bolt to existing holes in the truck frame rails.
Depending on what truck you have and which custom kit you get, you may need to drop the fuel tank and a heat shield in order to bolt the brackets to the inboard side of the frame rails. For some trucks, Reese makes an installation kit with brackets that bolt to the outboard side of the frame rails. The only thing in the way will be the spare tire. If available for your truck, that is the way to go.
Trailer hitch, hitches and bike rack (800)298-8924
usually has the best prices on the hitches. Their web site also has some videos of installations being done. You will need a rather hefty torque wrench.
I was 71 years old when I installed mine, and I am nit a mechanic. You can do it.