If your Nano S is not initialized go to https://www.ledgerwallet.com/start and follow instructions.
Once your device is initialized:
To manage your Bitcoins, you must launch the Ledger Wallet Bitcoin Chrome application. If you didn't install it yet, this is the way to do it: in your Chrome browser, and install the application here.
1/ Connect your Ledger device
2/ Enter your PIN code
3/ Open the Bitcoin app on your Nano S (right click)
4/ Launch your Bitcoin Chrome application on your computer
5/ Click on "Send", a popup opens
6/ Fill in the required fields: amount, recipient address you can paste or scan, level of fees
7/ Click on the "Send" button
8/ Your Nano S requires your manual consent to authentify this transaction: press the right button (above the "V" check icon) to confirm once you have verified the details of your transaction are right and wait until your Chrome app displays "validated"
9/ Your transaction is validated and will be tracked on the Blockchain as soon as it is confirmed by miners in accordance with Bitcoin protocol.
While waiting for this confirmation, your Ledger device can be disconnected as your transactions are tracked on the Blockchain. These transactions will be synchronized on your wallet when you open it.