Supply is how much companies can sell something demand and how much buyers will pay for it/want it. If something can not be sold very easily (like buying a product with a low production rate) but many people want it, supply and demand make the object's price rise, as people are more willing to pay for it. If something is very easily obtained/sold, or if something is not bought by many people, its price will go down, as store owners/companies want to get rid of it so they can sell something else that has a higher demand.