There are different definitions of price. Perhaps the simplest definition is to say "price is the value of a product (good) or service". A price is expressed in other goods, services, or in money.
Here is an example about price: Peter raises sheep for their wool. Sally raises chickens for their eggs. Winter is coming, so Sally wants to make a warm wool coat.She first measures how much wool she needs for a coat. She thinks she needs the wool from 2 sheep for the coat. She then goes to Peter and asks him what he wants for the wool she needs. Peter then tells her the price he is asking for his wool. Sally might trade some of her chicken eggs for the wool.