For sample case, you're need a printed promotional bags.
First Option :
Go to, bags vendor. Order it. The bags vendor will made the bags you want. And then vendor will go to printing company to print it. After all process finish, you have a printed promotional bags from a vendor.
Second Option :
Go to printing company. Order it. Printing company will order bags from vendor as your specification. After bags finish, printing company will print on it. And you have a printed promotional bags from a printing company.
There is a cooperation between 2 kind of business. One need each other, but as customers you choose which one you like. And compare the price of course.