It is good practice when leaving your office to lock your computer. This is most often done using one of the follwing methods. This will not close your work or "log you off" - this simply sets the workstation so you have to enter your username and password to access the data.
1. Simply hit "CTRL-ALT-DELETE" on the keyboard at the same time, then and choose "Lock Computer" with your mouse (Lock computer is the default so you can also just hit "Enter" on the keyboard).
2. Simply hit the windows key and the letter L at the same time.
Once you have sucessfully locked your workstation you will see the login window (will look similar to image below).
To access your files and applications - log in as normal.