How to connect bluetooth devices to Raspberry Pi

First of all you need a bluetooth dongle to plug into a USB port of the Raspberry Pi. Bluetooth Dongles are USB network adapters that allow a computer to communicate with Bluetooth devices such as cellphone, headphones, mouse, keyboards and so on.

You can check if the Bluetooth Dongle is recognised by the Raspberry Pi by opening a terminal window and typing the command:  

lsusb

This will list all the connected USB devices. Now give the command to install bluetooth support, utilities and tools, and a GUI Bluetooth manager.

sudo apt-get install bluetooth bluez-utils blueman bluez

It is not necessary to restart the Raspberry Pi and we can check to see if the bluetooth is live by running the following command:

sudo service bluetooth status 

or

/etc/init.d/bluetooth status

If everything went right, you will read this message in the terminal window

[ ok ] bluetooth is running.

Now we already have the drivers installed and ready to work with them. You can scan for devices using the command in the terminal window

hcitool scan 

If your Raspberry Pi does not recognize the connected USB Dongle, you will read the error message

"Device is not available: No such device"

The Raspberry Pi is very meticulous with the compatibility, not all adaptors work, please check this USB Dongle Support list , it depends on the manufacture and the chipset that is used.

Loading the GUI Bluetooth manager
From Raspbian's GUI select Preferences->Bluetooth Manager, a Bluetooth Devices window will pop up.
If you use Ubuntu Mate 15.04 go to the Control Center and you will find the Bluetooth Manager. From here you can search for and pair with devices, send files!