Stock is the basis for all soups. It can be homemade from beef, chicken, fish, vegetables, miso, soya, pork, lamb, Spices and herbs. Different styles of cooking have different recipes for stock suitable for their own type of soups. I have published a recipe for homemade chicken stock in this blog just check out the labels and archives.
If you have not the time to make your own it is a good idea to use ready made stock cubes. You can buy all types here the UK. Usually they are dry cubes that you crumble and add water to such as Oxo Cubes or dry stock mixtures such as Swiss Bouillon which you add to water. Some stocks can be purchased as concentrated pastes which you add to water and then use in your soup recipes. In some supermarkets you can buy a pint packet of ready made stock.
Look out for Organic stock products often more expensive but can have a better flavour and are pesticide free.
I hope this has revealed some of the mysteries of Stock.