Upon purchasing, you will receive a Private Download Link in your KVR Profile. Use this link to download the .ZIP file containing the instrument.
You will need to extract the .ZIP file using whatever archive program you like. I recommend moving the unzipped folder to wherever you normally keep your libraries and samples.
To open the Library, drag the .NKI file into the Kontakt window, or use the Open command within Kontakt. You don't need to use Native Access or the Add Library functions to open the .NKI.