Today, the sharing of information is becoming more and more an activity in full effervescence, hence the need for computer scientists to master this universe which is nowadays unavoidable. Networks are becoming more and more important because they allow to minimize the costs of information transport. They also allow to reduce the time of information circulation. This small guide does not have the vocation to approach all the concepts relating to the computer networks, but we just made a selection of the essential concepts which can make it possible to a user or a data processing specialist to create and manage a small computer network without much sorrows. It will consist in showing the readers how to link several computers in order to share software resources, hardware resources or data.