The document defines a computer as an electronic device that can manipulate and process information for more useful outputs. It describes different types of personal computers including desktop PCs, laptops, netbooks, and PDAs. It then discusses the common parts of a desktop computer, including the system unit/case, monitor, mouse, keyboard, and ports. The system unit contains all the essential computer components and can come in various form factors like full tower, mid tower, or slim cases. Factors to consider when buying a desktop monitor include the manufacturer/model, screen size/resolution, ports, contrast ratio, and response time.