To answer part of the question, depending on the odor they’re trying to catch, it could just involve storing an article of clothing with that smell on it. For others, it will be more complex.

Why? Need to train dogs with the types of smells you want them to track. If you teach a dog to alert on drugs, he won’t alert on explosives. You have to give them the range of types of smell you want. It is possible, for instance, to train dogs to help detect natural gas leaks on pipelines (before the additive is put in) but that takes a lot of high end training and a dog with an excellent nose and a lot of drive.