how do you set up a Logitech bluetooth mouse

Most mice come with their own dongle that is USB-3.0 or 2.0, but not USB 3.1/C. The dongle is prepaired with the mouse, if you prefer to use that, and use your Mac's built-in bluetooth for other things. Otherwise Go to Apple menu -> System Preferences -> Bluetooth, and pair it via the settings there. Make sure the mouse power is turned on. The dongles on most mice come in the underside in a door you can either open with a coin or slides off. You will find typically the dongle in one hole, and the battery in another. All MacBook Airs have built-in Bluetooth support.