If purchased on Blender Market or Gumroad:
Log in to your account on Blender Market, Gumroad or Flipped Normals.
Download the file named Outliner_Pro.zip.
Save the file to a convenient location on your computer (do not unzip the file).
Open Blender.
Go to the top menu and click Edit > Preferences.
In the Preferences window, navigate to the Add-ons tab.
Click the Install button in the top-right corner.
Locate the Outliner_Pro.zip file and select it.
After installation, check the box next to Outliner Pro in the addon list to activate it.
Drag and drop the addon Zip into the Blender window.
A prompt dialog should appear, set your desired repository if you want and then choose "OK".
New buttons should appear over the Outliner, if you can't see them scroll the header dragging with your middle mouse button.
You can set the preferences in the Add-ons tab of the Preferences Window if you wish, also you can access those settings via modifier keys like "ALT + Click" on the buttons.Â