Work wirelessly
Using Bluetooth® technology, your iMac can wirelessly connect (that is, pair) with devices such as the included Magic Mouse 2 and Magic Keyboard, and with optional devices like the Magic Trackpad 2, the Magic Keyboard with Numeric Keypad, peripheral devices, wearable sport accessories, and others.
Some included accessories may already be paired with your iMac. For more information about accessories, see the next section, 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 Bluetooth icon 
in the menu bar, then choose Turn Bluetooth On or Turn Bluetooth Off. Your iMac comes with Bluetooth turned on.
Tip: If you don’t see the Bluetooth icon in the menu bar, you can add it. Open System Preferences, click Bluetooth, then select “Show Bluetooth in menu bar.”
Learn more. See the Apple Support article Using a Bluetooth mouse, keyboard, or trackpad with your Mac.