This is an example of the GUI v Terminal
First Up is Synaptic Package Manager:
Enter the Synaptic Package Manager via System > Administration > Synaptic Package Manager
Do a search for "Wallpaper Tray"
Right click and select "Mark for Installation" then click "Apply".
The program can then be found under Applications > Graphics > Wallpaper Tray.
Then there is the Terminal
$ sudo apt-get install wallpaper-tray
Synaptic is a nice tool for browsing and very friendly to new windows natives. In this case it is quiet clear which is faster.