It would help if we knew what device you need help with, most phones and tablets if you place your finger at the top of the screen and swipe down there you should see the Bluetooth icon just press it on, or you can also go to settings then connections, select Bluetooth toggle it on and pair any of your devices.
Try swiping down from the top of your screen and then you should see the Bluetooth symbol, press it once to turn on or hold it for a few seconds to shortcut straight to Bluetooth devices