Homeopathy was developed in the early 1800's by Samuel Hahnemann. As in vaccinations, you receive a dose of what you're trying to eliminate.
All homeopathic remedies are natural, derived form animal, vegetable or mineral matter.
Illnesses are treated according to their symptoms. It doesn't matter where you got the cold, flu, diarrhea, muscle cramp or headache. How it is manifested is what a homeopath looks at. For instance, a cold can come on slowly or quickly, make you thirsty or not. A headache can be in the front or the back of the head.