All the above discussion is correct for the old-fashioned kind of rivet with a protruding head. This is probably the correct kind of rivet head for V-2 missiles and other older designs, but be aware that flush-headed fasteners are also widely used.
A flush-headed rivet or bolt leaves the outer surface flat, and does not mess up the aerodynamics as badly. These fasteners do, however, show from the outside as a small circle, and often have a slotted head or a small central dimple (from pulling the stem out of a blind fastener).
These can be added to your model by using a small piece of tubing with a sharpened lip. Press it into the paint as it is drying and it will leave a small round mark that looks like a flush rivet head.
Mind you, I am telling YOU to do this, because there ain't enough $$$$$ in the world to make ME sit down for hours and do this!