A canvas that is already right
The PNG is the full bleed box at your resolution (2063 x 3150 px for a standard comic at 300 DPI) with the bleed edge in red, the trim in black and the safe area in dashed cyan. The PNG records its resolution, so Photoshop and Clip Studio open it at the printed size rather than at 72 ppi. Open it as the bottom layer, draw over it, hide it before you export, or turn the guides off for a plain canvas with nothing drawn on it. The PDF is the same guides as vector lines with a TrimBox set, for layout software or for handing to a printer as a spec sheet. Inside a project the numbers come from the project; standalone, pick a preset or type a size. Presets with a bleed-free spine edge (KDP 6 x 9, IngramSpark) offer a right-hand and a left-hand template, because the guides sit differently on each; the drawing and page editors place them for each page automatically.
Questions
What size is a comic page template?
Trim plus bleed. For a standard US comic that is 6.875 x 10.5 inches, or 2063 x 3150 pixels at 300 DPI, with the trim and safe lines drawn inside.