Stock is a common and useful cooking ingredient. It makes a base for soups and can be used in cooking to add flavour (works especially well with couscous). Most people use the dried stock cubes, which are usually very high in salt, or buy premade stock.
However, stock is easy to make yourself. The next time you do a lot of cooking, save your scraps and toss them in a large pan. Put any vegetable offcuts, peelings, or stalks in. If you're cooking chicken, for example, toss in the carcass (all the bits you don't use in the meal). If you have them, tossing in some peppercorns and sprigs of fresh herbs can help add a nice flavour. Cover with water and let simmer for several hours. The more that you let it reduce, the stronger the flavour will be.
You can then freeze the stock to use whenever you need it. I like making vegetable stock and then freezing it in ice cube trays. That way you have portion size amounts ready to use when you're cooking.
Making your own stock makes delicious stock, saves money, and is healthier for you.