When you buy a product you are entering a contract. But what is a contract? A contract is a legally binding agreement meaning it can be enforced by the law.

Example of this;
You want to buy a jumper that costs €20. You go to the check-outs and you offer the €20. The cashier accepts this offer of €20.

The consideration= The items of value that have been traded by the parties (you and the cashier), is you receive the jumper and the store makes a profit.

Contract