Manufacturers are associated with products, providing web site, contact, and descriptive information. Each product that is created is associated with a Manufacturer.
For stores where manufacturer information is not necessarily relevant, a default manufacturer is created upon installation.
It is not necessary to create manufacturers prior to creating your catalog. Products can be re-associated to manufacturers after all the product records have been created. However, creating the manufacturers first can save a lot of extra work if you already know that you will be using this information.