I'm most definitely part of the 90%.
I can get my computer to do everything I want it to - connect to the internet and create and print a Word document.
Most people, at least those of my generation, the 'baby-boomers', were never taught how to use a computer;
as a result, I have no real idea about all the things my PC, or even my Smartphone, is capable of.
I do have a copy of 'Complete Idiot's Guide to Computers' which I bought in a fit of enthusiasm about 10 years ago. I think I got to page 8 before deciding that I wasn't really interested.