I have iphone8 how do I set up the Bluetooth?

What are you trying to connect? Once you have a Bluetooth device you wish to connect to, such as a speaker or headphones, you must put them into discovery/pairing mode. Follow the instructions for the device to do that. Then on the iPhone, open Settings>Bluetooth, tap on that to turn that on.You should see a spinning wheel under Other Devices, and you should be able to "see" the device that you wish to pair. Tap on it and follow the on-screen instructions to complete the pairing. It should show in the list of My Devices, and say Connected. You can then use your Bluetooth device.