A placebo is a dummy medicine. Many people have reported improvements after taking a placebo thinking it was a real medicine. There are good reasons to think that homeopathic medicines are not placebos. First, they act on infants, animals and unconscious patients. Second, patients frequently report feeling worse (the homeopathic aggravation) before they begin to improve. This initial worsening occurs even when they have not been told to expect it.
Though we do not know how homeopathic medicines work, it is clear from the clinical results of the last 200 years that they do act to cure sick people. It should be mentioned that the pharmacology of most drugs is not completely understood which in no way keeps doctors from prescribing them.