If your Blue is not initialized go to https://www.ledgerwallet.com/start and follow instructions.
Once your device is initialized:
1/ Connect your Ledger device and power it on
2/ Enter your PIN code
3/ Open your Bitcoin app on your Blue
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 Blue requires your manual consent to authenticate this transaction: tap on "confirm" once you have verified that the details of your transaction are right, 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.