Besides creating albums composed of custom items (uploaded images and videos) it's possible to create albums that automatically fetch the items from different sources such as Joomla Articles, DJ-Classifieds Ads, DJ-Catalog2 Products, etc. This feature is handled with Album Source Plugins. To see the list of available plugins click on the Album Source Plugins button from the Control Panel and you will be redirected to the Plugin Manager. DJ-MediaTools package is installed with many source plugins. Make sure all the plugins are enabled otherwise you won't be able to use them.
Let's go back to the Album edit form and the parameter Album Source. On this list you can see Custom slides and all available Album Source Plugins. Selection one of them will open the additional parameters to set the source.
Note that each plugin has its own requirements such as specific extensions installed etc. If some of the requirements are not met you will see the proper message like on the screen below.