Pairing a smartphone with a Ledger means associate an iOS or Android mobile to receive push notifications to authenticate transactions. It doesn't mean you'll be able to use the Ledger directly on your mobile. To know on which OS you can use your Ledger device, refer to this FAQ.
If you downloaded the Ledger Authenticator application on your mobile and doesn't understand how it works, please read the Ledger Authenticator guide.
Note that this application is only required with Nano (not Nano S) and HW.1.