The basic construction steps for building the airframe of an aluminum airplane are as follows:
The various parts to make up a particular component are fastened together using Clecos through the pre-punched holes. (not all kits are pre-punched)
Clecos are temporary sheet metal fasteners that you insert through the rivet hole to hold the two pieces in place.
In some kits, the parts are pre-punched, so assembly is just a matter of lining up the holes. In others, the parts are clamped together using small clamps and careful measurements are taken to make sure the parts are in the right places before being drilled.
The pre-punched holes are drilled to final size using a high-speed air-powered drill. If the pilot holes aren't predrilled, then the full holes will have to be drilled between the two parts to be joined.
Since drilling through sheet metal produces sharp edges around the holes, each side (front and back) of each hole in each sheet of metal must be deburred with a quick turn of a deburring tool. (this is a total of 4 times for each hole drilled through two pieces of metal)
The outside edges of any metal part must also be smoothed and polished with a scotch-brite wheel, emery cloth, or a file to remove any rough or sharp edges.
Dimple or Countersink
A dimple is created around the hole for two reasons. First, it allows the rivet to sit flush with the surface for better appearance and lower drag. Secondly, it makes the connection between the two pieces of metal stronger because they nest together and resist sliding apart.
Dimpling can be done with a squeezer, a c-frame dimpling tool, vice-grip pliers with a dimple die welded to the jaws, or a pop-rivet type dimpler.
Very thick material is usually countersunk instead of dimpled, and some interior surfaces don't use flush rivets so they aren't dimpled or countersunk.
Priming interior parts before they are joined helps resist corrosion, but most aluminum parts are already coated with a thin, pure layer of aluminum (alclad) to resist corrosion anyway. Some people prime every square inch of interior metal, others prime just connection points between metal, and others don't bother priming at all. It all depends on your local climate, whether you are worried about corrosion or not, and how much weight you are willing to add to your airplane. Priming any non-alclad or steel parts IS required, however!
Finally, that last 1% of the work is the actual job of inserting a rivet through the hole and using a rivet gun or squeezer to smash the end of the rivet to hold the two pieces of metal together.