To access the Media Browser, click on View and then select Media Browser. You can also customize your toolbar and add a button or press Control-K on your keyboard to open it.
In ProPresenter 6, the Media Browser is only available on Windows.
To use content from the Media Browser, click and drag it to the slide that you want it applied to. Images, Audio, and Movies can only be added to presentation; you cannot use the Media Browser to add content to your Video/Image Bin.