Knowing was "megapixel" means is a pretty basic piece of information. It's at least a bit weird to not know that and yet want to provide sign making services to customers.
No personal offense intended by this, but anyone designing signs (especially anyone who actually sits in front of the computer doing the work) should have very good or expert knowledge of general computer issues, computer graphics and principals in graphic design. Having artistic talent and good design sense is really kind of crucial as well.
It's a pretty stupid situation if the average customer off the street has the same level of computer knowledge and design savvy as the guy laying out the sign design.
I whole heartedly agree with Bobby H... I would highly recommend you take some classes at your local community college. It would be a GREAT benefit for yourself and your clients..! Pickup up some books from your local library/ Barnes & Noble etc.