User preferences allows you to customize the behavior of the application for the specific user. To get to your user preferences either click on the triple gear in the top right corner:
or click "Settings in the bottom left of the screen. Either way you'll get to your preferences page shown as below. The preferences are on the bottom left and you can control things such as whether report totals in web reports appear before or after the data, which view is your default view to show when you log in, whether you see a view immediately upon logging in, and much more.
Below are examples of settings you can customize. The most common involves choosing a view as your home screen. To do so - first check the check box to activate the option, then where it says "Home Screen View" select the view you want to be your home screen view. Other options you can see will allow you to either show or hide the left hand menu by default, and whether you'd like to see report totals above or below the report for web reporting. Depending on your account status you may have more options listed below as well.