On Comicad you can either advertise, publish or both.
To advertise you only need an ad, by creating an ad alone you'll be advertising already since all ads are randomly displayed on available free slots. After that you may advertise your ad on paid slots or advertise on $0 slots.
To publish you need a site of your own where you can put a 1 line javascript code.
With a site of your own you can also exchange ads for free with other sites through exchange ad units.