When a computer is to be used by more than one person, or when you don't want anybody to sneak into your information without your knowledge, it is best to set up users, permissions and passwords in it. Setting up a user does not take much time, and, what's best, setting up has the great advantage of not allowing anybody to access certain part of the information unless he knows the access code to open it. It's like hiring a watchman for your computer.
It also allows an easy personalization, as each user will be able to have his own documents folders, his own graphical configuration, his own favourite links, etc.
Two kinds of users
There are two kinds of users in a computer: (standard) users and administrators. Users are usually able to do what they need to do within their section of the computer (read/open their documents, check their email, play music, create graphics, save photos, etc.), but they are not able to change much (and by 'much', I mean install or remove software, change global configuration settings, even turn off the computer in some cases) if they do not have the permission to do so.
It is great to use your computer as a standard user if you don't know much about them. That way you will not be able to ruin it!
Administrators can check and change the users' configuration and permissions, review all the files, install and remove software, etc. This is to say they are in control of everything that happens in the computer.
Yet being an administrator may have a disadvantage too: Administrators sometimes need to "babysit" the computer, help all users with their configuration problems, tweak the permissions when needed, install the applications users need, and the like.
Under the Windows operating system all users are administrators by default. Under Linux operating systems all users are users by default, and there is one "super user" for administration tasks. All operating systems can add and remove users easily.
Adding, changing and removing users
Under Windows, you can add, edit and remove users by going to your Control Panel and clicking on the respective link. I have already mentioned what are the differences between an administrator and a user, so you shouldn't have problems.
Under Linux there is one additional thing to mention: users can be grouped. A group means some users will be related to each other and may have some access between each other's files if the administrator authorised them to do it. Needless to say, users in different groups will not have this permission that easily.
Knowledge + Computers