Three boxes, one canvas
Every print page is three nested rectangles. The bleed box is the whole canvas you export. The trim box is the finished page after the guillotine. The safe area is inset from the trim so a cut that drifts a few hundredths of an inch never clips a balloon. Your drawing software needs the bleed box in pixels; your printer needs the trim size and bleed amount in inches or millimetres.
Formula
Bleed width = trim width + inner bleed + outer bleed. Bleed height = trim height + top bleed + bottom bleed. Pixels = inches x DPI, rounded up so you are never a pixel short. A 6.625 x 10.25 in comic with 0.125 in bleed is 6.875 x 10.5 in, which at 300 DPI is 2063 x 3150 px and at 600 DPI is 4125 x 6300 px.
Common sizes
US comic 6.625 x 10.25 in. Manga tankobon roughly 5 x 7.5 in. Magazine 8.5 x 11 in. Trade paperback 6 x 9 in. See the full list, with printer-specific variants, on the print presets page, and the background in standard comic book page sizes.
Questions
What size is a standard comic book page?
The US standard trim is 6.625 x 10.25 inches. With 0.125 inch bleed the art canvas is 6.875 x 10.5 inches, which is 2063 x 3150 pixels at 300 DPI.
Should I draw at trim size or bleed size?
Bleed size. Set the canvas to trim plus bleed and draw guides at the trim and safe lines. Exporting at trim size forces the printer to scale your art up.