If your Nano or HW.1 is not initialized go to https://www.ledgerwallet.com/start and follow instructions.
Once your device is initialized:
1/ Connect your Ledger device
2/ Launch your Bitcoin Chrome application on your computer
3/ Enter your PIN code, your Bitcoin wallet opens
4/ Click on "Send", a popup opens
5/ Fill in the required fields: amount, recipient address you can paste or scan, level of fees
6/ Click on the "Send" button, another popup opens
7/ Your Chrome application requires a second factor of authentication to authenticate this transaction: you can select to do it with your security card (provided with your device), or to do it with one of your paired smartphones. Select the method you prefer and go through this 2FA step following the instructions.
8/ Wait until the transaction is validated. Then it 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.