How do you use (run/install) an AppImage?

AppImages do not need to be installed. They are a self-contained app that simply needs to be made executable and then run.
As nothing is actually installed, it is good idea to move the downloaded 
APPIMAGE file to a folder of your choice before creating any shortcut link to it.  For my Fedora install I use /usr/local/share/filename-directory. If necessary I will also save the shortcut image here.
Download the AppImage and then make it exscutable as follows:
$ chmod a+x Filename.AppImage
Now run the application as follows:
$ ./Filename.AppImage
When first run, some AppImage applications will ask if a desktop shortcut should be created.
If a shortcut is not created, this can be done manaually using your text editor of choice. In my Fedora install this is done here: ~/.local/share/applications/