Computer Science is the science of using computers to solve problems. Mostly, it involves designing software (computer programs) and addressing fundamental scientific questions about the nature of computation but also involves many aspects of hardware and manufacturing the large computer systems that form the infrastructure of commercial and government enterprises. Computer scientists work in many different ways: pen-and-paper theoretical work on the foundations and fundamentals, programming work at the computer and collaborative teamwork in doing research and solving problems.
Common misconception about Computer Science
Computer Science is not about using spreadsheets, words or image tools. Its true some application difficult to master like Photoshop or Excel and many jobs depend on expertise of using such tools ( applications ). But computer science is not about using the tools, playing games, writing content on websites, assembling or dissembling of hardware, or knowing which computers are best to buy.
"Computer Science is no more about computers than Astronomy is about telescopes" - Edsger Dijkstra
Computer Science is about building the software packages, algorithm behind the games, about the technology behind Internet and about creation of computing device.
Computer Science vs Information Technology
While computer science has become a somewhat precise term as a field of study (like geology) on other hand information technology (IT) is a somewhat a different term. The commercial world uses the term IT in a variety of contexts, mostly, to mean "anything to do with computers". Many business uses this term to refer specifically to the combination of databases, information processing systems and communication systems (email, web browsing) they have been installing in the 80's and 90's. Thus, an IT job could mean a sales job in a computer company, or a business manager overseeing the installation of software, or it could mean a network technician who installs fiber-optic cable, or of course a software engineer. However, computer science generally denotes a professional with computer science training, one who is involved in the creation of software and software systems.