If you use Stumbleupon, never, but never add 'comics' as something you want to browse. You get sites about actual comics, but you also get the absolute worst hack webcomic shite.
It doesn't matter if you can't draw, just stack two circles on top of one another in MS Paint and away you go! People will think it's charming and homemade! You definitely don't need jokes, only those bullshit hacks who make money money from their comics bother about shit like structure and punchlines.
Here's my guide to making a webcomic: