You will need to enter the main container width of your website, you can simply use this tool to measure it.
This is a very useful option in case you want to limit the ads appearance based on users screen width, to do so simply add this minimum width and your ads will not be called on this screen width and below.
Sometimes you will need to add margin to your ads to tune the position a little bit, you have "left, right and top" margins to adjust dirctly form the panel.
Using the native WordPress media uploader you can upload your custom banner image, and the plugin will detect its height and width automatically, you can assign a custom link to your image banner, or simply use '#' to unlink it.
You can add any publisher code, including Google Adsense, but make sure to enter the ad unit width and height, it can't be detected automatically, and it's recommended to use the fixed size Google Adsense units, not the responsive ones.
Just as the right and left banners settings, except that the mobile banner will be shown on any mobile devices (i.e. tablets and phones).