If you have never used chicken bouillon, its just dehydrated chicken broth. This is how the soup gets most of its flavor so you must use it.
There are many different brands out there such as Maggi, Knorr, etc. We usually use Knorr and you can find it at the grocery store, in the spices section.
Bouillon cubes are a popular thing to use in the UK for many of the foods they make. Its very concentrated, and high in sodium content so try not to overdue it.
The bouillon is what gives the broth the yellowish tint that you see in chicken soup. This is one ingredient you don't want to forget from the store so be sure you have a grocery list.
