Hi, Dave,
(This answer assumes that you're using the Xfce version of Salix 13.1.2). Don't worry; it's not a dumb question and fortunately, it's very easy to change the wallpaper. There are a couple of methods to do it:
First, download the wallpaper(s) you're interested in and save them somewhere in your /home folder, or in your Pictures folder, or even in a newly created Wallpaper folder -- it's your choice where you'd like to put them.
Next,
1. Go the main menu (labelled "Salix") in the lower left-hand corner of the taskbar.
2. Choose Settings.
3. Choose Desktop (under the Xfce 4 Settings Manager).
4. You should see a window like the screenshot shown here:
http://img836.imageshack.us/i/xfcedesktopbackgnd.png/
5. Click on the green "+" (plus) button to navigate to the folder where your wallpaper is and select it.
Alternate method:
1. Right-click anywhere on your empty Salix desktop.
2. Choose Desktop Settings.
3. You should see a window like the screenshot above.
4. Click on the green "+" (plus) button to navigate to the folder where your wallpaper is and select it.
If you're new to Xfce and want to learn some of the basics about this desktop environment, you might want to download the
PCLinuxOS Magazine special issue on the Xfce DE. It is mostly distro-neutral and is a good starting point:
http://pclosmag.com/index.php/downloads
(Look for the "Gtk Lightweight Desktops: Xfce & LXDE S[pecial] E[dition]")
HTH,
=david (another PCLOS user who's having fun with Salix OS)