These are meant to be used with
the_post_thumbnail() function. The sizes are defined on the Manga+Press Options page, under the Comic Page Options tab.
comic-page Creates a "Comic Page" image from the uploaded comic. This image size would be used to display your comic.
comic-admin-thumb Creates an 80x60 thumbnail for the Comics page in the WordPress admin. This is a private image size that is only used in the WordPress admin.