If you don't want to read the government's Occupational Handbook (I think it's your best bet -- job descriptions are going to be dry no matter who writes them), then we can start from the top. At the highest level, I think computer-related jobs can be broken down into two groups - those that are concerned with software development and those that aren't.
Software developers create applications and programs using programming languages like Java, C#, C++, C, and many more. Typically, these people work as programmers or software engineers. In terms of education, they usually have degrees in computer science, software engineering, or computer engineering.
Non-software development jobs deal with technical support, network design, IT management, and other jobs that are concerned with supporting, maintaining, and upgrading a company's infrastructure. Many of these jobs require certifications and possibly degrees in areas like management information systems and information technology.
Each of these areas can be further subdivided into more specific groups. I'm a software developer, so if you have any specific questions about that line of work, I can try to answer them. As for the non-software development jobs, someone else working in that position could probably give you a much better description. Maybe you should have asked forum members to describe their own jobs -- that might be more beneficial to you.