Back in the heyday of text-based operating systems like Unix and DOS, the command prompt was the operating system, and not knowing how to use it meant that you could not really use your system without someone experienced in computing holding your hand. This was the era of computing clubs, when getting to grips with your computer required some serious devotion and learning.
When the most successful graphical operating systems, the various Apple Mac and Windows incarnations came along, they triggered a massive increase in the popularity of computers by simplifying the whole process of using them. No longer did users have to memorize reams of commands in order to simply configure and navigate around their computers.
Slow computer got you down? Maybe a hardware upgrade should be in your cards, if so this guide to the Fundamentals of Upgrading a PC is an invaluable read. PCSTATS Tips