Homeopathy was devised by the German Samuel Hahnemann in 1796, long before the discovery of germ theory – but after the discovery of vaccination - so medical knowledge was still in its infancy. Hahnemann believed that “like cures like” and that the smaller the amount of a given substance administered the stronger it's interaction with disease. If pepper causes sneezing, a tiny amount will therefore cure sneezing, and the smaller the amount given the more potent it will be.
In order to deliver such minute quantities, homeopaths repeatedly dilute the substance in water. For example: mix 1g of pepper in 100ml of water; extract 1ml of water from that and dilute it into another 100ml of water (now it is 1g of pepper in 10L of water). Repeat this process 20, 30, or 100 times (Each dilution is called 1C and is in effect adding 2 noughts on the end of the ratio). At each dilution, the water jar must be struck against a leather-bound book, preferably a Bible, in order to 'potentize' the mixture.
There is no evidence that after just 10 dilutions (1g in 10,000,000,000,000,000,000 litres, or equivalent to diluting it in the Pacific Ocean) that any of the original substance is detectable, never mind at 30 or even 100 dilutions. To get around this, homeopaths claim that water has a ‘memory’ so it is able to remember the original active molecule. Strangely it is unable to remember all the poo it has had in it. Homoeopathy is one of the most obviously ridiculous pseudo-medicines and it constantly shocks people when they find out how it is actually made. Explaining the dilution process is one of the best counters to anyone who suggests you 'try it, it worked for me'.