You might specify what kind of lan you have? Assuming you have windows NT or 2000 notwork, You will typically have a server and several workstations.
You need to know administrator password first to create and control other users. After you log into the server as administrator, you might go to the administrator tools folder in the start menu, where you will find active directory and user settings.
This is the place where you can create a user and can change their security settings. You can play with these settings creating dummy user. Microsoft has vast knowledge base in their site on this topic. You might read the same to get familiar with the concepts.
