Volume & Supply and Demand

Hi guys, there's something that confuses me alot and hope to have some insights Price moves base on Supply and Demand, if there's higher demand than Supply, price will rise and vice versa. Meaning if the market has a high demand of a stock of apple, and there's not enough Supply, price will increase And we also know for volume, it represents the amount of transaction that occurs (i.e if volume says 100, that means 100 shares were bought and sold since every 1 share/unit bought would need to have 1 willing seller) In essence, if every unit needs to have an equal buyer and seller, how does price essentially rise? Since I can't buy 100 shares if no one is willing to sell 100 shares to me and vice versa Hope this isn't too confusing