Installation
Just go to Blender Preferences, click install and choose the zip file.
In the addon preferences there are some options you might want to change.

Usage
After installation you will have a new panel in the PowerSave category in the list of addons on the right of the 3D view (opened by pressing N on the keyboard).
There you'll find a path, from which PowerLink will load blend files.

Below it, the list of blend files, a checkbox, and a button.
The checkbox is for advanced mode, which allows you to import from multiple blend files at the same time.
The button refreshes the list of blend files, though since this is done automatically when you change the path, you won't need it often.

And below that, another list, this time for collections in the chosen blend file(s).
It has the same checkbox and refresh button.
The checkbox allows you to import from multiple collections at the same time.
The refresh button is only necessary when using advanced blend file mode, where the collection list doesn't refresh automatically.

At the bottom of the panel is the PowerLink button, and to the right of it, the append version.
Linking will add collection instances on the 3D cursor, appending will add objects and move them appropriately.