The cover preview provides a first look at your efforts. You may see potential faults and remove them by clicking at Back to redo some steps of this process again.
If you are satisfied with the result you are ready to print. There is also the alternative to print your cover with cutmarks (in top left-hand corner in the picture below) to cut it out easier.
The actual printing process starts by clicking at the Print button upside the preview windows.
If you want to adjust your printer first (especially if your first results weren’t satisfying) click on Printer adjustment first (at the upper right of the picture). See here for more details!