Demand: how many people want to buy, and how badly. If lots of people want a particular figurine, demand is high.
Supply: how much there is to sell. If the factory only made 1,000 units, that's all the market can buy—supply is limited.
🔆Picture price as a seesaw: on one side sit "the people who want to buy" (demand), on the other "the goods available to sell" (supply). Whichever side is heavier, the price moves that way.