Work wirelessly
Using Bluetooth® technology, your iMac can wirelessly connect (that is, pair) with devices such as the included Magic Mouse and Magic Keyboard, and with optional devices like the Magic Trackpad, peripheral devices, wearable sport accessories, and others.
Some included accessories may already be paired with your iMac. For more information about accessories, see What’s included.
Connect a Bluetooth device. Turn on the device so that it’s discoverable, then open System Preferences and click Bluetooth. Select the device in the list, then click Connect. The device remains connected until you remove it. Control-click a device name to remove it.
Turn Bluetooth on or off. Click the Control Center icon 
in the menu bar, click the Bluetooth icon 
, then click the control to turn Bluetooth on or off. Your iMac comes with Bluetooth turned on.
Tip: You can add the Bluetooth icon to the menu bar. Click the Bluetooth icon in Control Center, click Bluetooth Preferences, then select “Show Bluetooth in menu bar.”
Learn more. See the Apple Support article Using a Bluetooth mouse, keyboard, or trackpad with your Mac.