Turn on the device by switching it to ON mode, and it will enter pairing mode (you will hear the word Pairing through the headphones), and the LED will flash red and blue alternately.
Now, go to the settings of the device you want to connect your headphones to, enable Bluetooth, and find your SPC DREAMER 2 PRO in the list of available devices.
The SPC DREAMER 2 PRO can connect to two devices simultaneously; to learn how to do this, you can check out the article Simultaneous connection with two devices.