Hmm well there's a lot of stuff you have to do to turn something from your sketchbook into an online comic and you have to be pretty familiar with all the programs involved in doing so. In other words it'll take a lot of time if you don't know how to use some of the programs.
Anyways here's how I usually turn paper into an online digital picture.
1. Scan your picture and either saved it and open with photoshop or just import it directly into photoshop.
2. Set up your comic how you want it to look when your done(I'd use the lasso tool and the move tool in photoshop to move thing around.
3. Trace your picture via Pen Tool
on a new layer and make sure that only your new line art shows and not the original after your finish.
4. Alright now that's the lineart i finished you can work on coloring however you want. I do suggest that you use a new layer to color so that you don't mess up your new lineart.
For coloring I would look around for tutorial for different style of coloring since it all depends on how good your skill at coloring are at the moment and whether or not you would want to pump out comics by the truckload or just take it one page at a time.
If your new to photoshop and coloring on the computer I suggest you useCel Shading
and work your way up from there once you get use to trying other coloring styles.
Well that's the basic step to it and all you need for this is a computer,scanner,photoshop, a mouse and some patiences
For photoshop you can buy it basically anywhere that sells programs and such. Also there's a few more steps that I usually take when I do my pictures that involves other programs and tools and if you can't get photoshop basically any program that allows for layering, the pen tool and select tool will do such as flash or illustrator but photoshop is the one you want for coloring pictures.