Basic wiring and mechanical skills are required, but not hard to do.
Cruise control works by monitoring vehicle speed, on newer vehicles there is a VSS(vehicle speed sensor), or you can add a VSS just for cruise control to the drive shaft.
Second part is the actuator, this runs off engine vacuum and has a cable that connects to the throttle.
Third part is the on/off/set and safety cutoffs, wires to steering column for on/off/set and wires to brake light, and clutch or Neutral switch depending on type of transmission, this cuts off cruise control if brakes are applied or clutch is pushed in, or automatic is shifted to Neutral/Park.
This is a PDF from Rostra, they make add on cruise controls, I haven't use one before, but it has diagrams and pictures of the install process:
I would check reviews of any product you may install