When you find a company that provides book printing service options for your project, you need to make sure that you have all of the right files so that they can complete the project. If you do not give them all of the information that they need, they will not be able to print your book. This begins, of course, with the actual text that you want to have printed. They will want to see this in a hard copy so that they can go over it, but they will also want an electronic copy for editing and printing purposes.
You will need to give book printing companies all of the graphics that you want to be used on the cover. If you have a full cover design, that is even better. Many companies will allow you to select a generic design or to work with them to create one, but this does not guarantee that you will get a cover that looks just the way that you want it to look. If you bring your own, you will be much more pleased with the final results.
Lastly, you need to have any photographs or other types of images that you want to use. This could mean a photo of yourself for the back cover. It could mean drawings that you have done to be used as illustrations. The book printing company will need to see all of these so that they can integrate them into the finished product when they print it.