The Bluefruit LE Friend USB-to-BLE board makes it easy to get your computer talking to your BLE enabled phone or tablet using a standard serial/UART connection.
In it's simplest form, it works on the same principle as a common USB/Serial adapter. Any data that you enter via your favorite terminal emulator on your development machine will be transferred over the air to the connected phone or tablet, and vice versa, as a basic 'UART' connection
You might be asking, Hey my macbook already has Bluetooth and I can get a USB Bluetooth adapter, so why use this? Good question! Windows 7 doesn't support Bluetooth Low Energy natively, and on Win8 or OS X you'll have to sort through a huge pile of native Bluetooth APIs and development tools that often require an annual paid license and specific license terms to access. You can't just connect wirelessly without a huge stack of software or firmware in the way because there isn't a standard, open source, cross-platform way to talk BLE today.
The Bluefruit Friend is much more, it has a full BLE peripheral stack and interface software so that you can treat your BLE connection just like a UART connection - that makes it trivial to use with free Terminal software or scripting software like python (with pySerial). Using Bluefruit LE Friend, you can be up and running in under and hour on just about anything with a USB port, with easy migration across platforms and operating systems.
To use, simply plug into your computer and flip the switch to either UART mode (transparent data transfer, anything you type will be sent, and data from phone is received as well) or CoMmanD mode, where thanks to an easy to learn AT command set, you can also create you own basic GATT Services and Characteristics, simulate Beacons, and change the way that the device name appears/advertises itself.
To make sure that your device stays up to date and can benefit from the latest Bluefruit LE firmware from Adafruit, you can also update the firmware on your BLEFriend over the air using any BLE-supported iOS or Android device. One of the biggest advantages of the BLEFriend and the entire Bluefruit LE family is that Adafruit write and maintain all of the firmware running on the devices themselves from scratch and they'll be releasing new firmware and bug fixes without having to rely on a third-party vendor. For super-advanced users, there is an SWD connector on board that can be used to reprogram the nrf51822 using Nordic's SDK and an SWD debugger .