Dog collars are essentially a basic form of restraint owners use to keep their dogs under control and comply with local laws that require dogs to be leashed and tagged. But dog collars can apply damaging pressure to your dog's neck and damage his skin, tissues and even cause breathing problems. A harness is generally considered to be a safer method of restraint than a collar, but collars still serve the purpose if you use them correctly and safely.
Place a collar around your dog's neck. It is safest to use a flat, limited slip collar that has a quick release snap you can disengage quickly if your dog gets into a dangerous situation while wearing his collar. Limited slip collars will only tighten to a certain point on your dog's neck and will help prevent accidental injuries due to pulling in the event your dog tries to escape while restrained.
Adjust the collar so you can fit at least two fingers comfortably between the dog's neck and the collar. The collar should not be so tight that it could cut into your dog's skin nor should it be loose enough that your dog could slip out of it and escape while out on a walk.
Attach the collar to whatever object you are planning to use to restrain your dog. In most cases this will be a leash or tether of some kind. Make sure the clip on the end of the leash closes completely and your dog can not slip off the leash.