Hew guys!
I want to build an overdrive/distortion pedal, just for the fun of it and the learning experience.
I have no prior knowledge - is there any website/guide to get me started? A-Z, including the theory(such as which part does what?)? Thanks!
This isnt so much the technical side of things, but this might help - it's certainly informative.

Ball Custom Mark I

Korg Pitchblack > Dunlop Crybaby wah > mODDball audio Green Bastard > Marshall GV2 Guv'nor Plus > EHX Holy Stain > MXR Phase 90 > MXR Carbon Copy

Jet City JCA20h
Epiphone Valve Jr.
Blackstar HTV212
Here's the very best place to start understanding the parts of a circuit--start with boost and work from there:

There's so much info out there, as people are posting. But frankly, 95% is organized terribly and not presented in a format that's conducive to learning for noobies. The beavis audio site is top notch in that regard. Once you get into the basics there (and google basic electronics) the geofex articles are an decent second step.