When you first get a new computer or load an Operating System (such as Windows, OS X, or Linux), typically you need to set up the user accounts for the machine. The purpose of user accounts is two-fold: they allow for unique settings to be applied when someone signs in (i.e. custom desktop background and shortcuts) and they set the level of administrative functionality allowed for an account. The second factor is the more important of the two because it helps keep your machine’s contents safe from others that might try to do harm.
In Linux, the default user is never the administrator (also known as Root). Unfortunately, in Windows and OS X, the default user is an admin, which means that if someone else gains access to your account or some malicious software executes while you are signed in, you might be in a whole lot of trouble. I go step by step through the process of creating a new user account in my book, but the User Accounts tool in the Control Panel (the computer’s settings) is where you want to go to get started.
It is important that you 1) create a unique account for each regular user of your computer, and 2) allow for only ONE administrator account on the machine which is only used to do administrative tasks (like install new programs and do high level computer maintenance). For everyday computer usage, one should never be signed in as an admin. They should, instead, be logged in as “normal users” that don’t have the ability to install software and do other powerful things that could be dangerous.