You do not normally need to log out of this service.
However, if you are using a shared computer you can log out and remove the cookie from this computer. This will not affect any other cookies stored on this computer.
What's a cookie?
The cookie is a simple text file stored on your computer that records your user number but not any personal information such as your username or password. The web site uses this information to retrieve your own personal profile each time you return to the site.