This template may help.
On a printing press, artwork is printed on a larger sheet of paper and then trimmed. This is a mechanical process, so there’s always the possibility that the paper will move slightly. These small movements of the paper during the trimming process can leave a distracting white border your design unless the artwork is designed with bleed.
Comic book cover art is printed all the way to the edge of the page, so artists add a .0125 inch-wide bleed on all four sides of your design that can be cut away during trimming. This discarded area falls outside the trim line. This should be a continuation of your design so that no matter where the cut falls, it will look the way you want. (If it helps, think of this bleed area like the extra bit of pie crust that gets cut away to make a perfect homemade pie.)
Download this template to help you design with bleed.
To be absolutely certain that nothing important is cut away, keep all important elements of your design (like your name and the comic book’s title) inside the Safe Area, .25 inches safely away from the outside edge.
One final note: Winning comic book covers will be printed at 6.69 x 10.25 inches. Remember to use fonts that will still be legible at this reduced size.