Wireless keyboard and track pad in one
The power button for the Trackpad is on the right hand end of the battery case. Press that button to initiate the pairing process. On the top of the Trackpad just above the power button is a tiny green light (you probably cannot see it unless it is lighted). That light will indicate ehther or not the Trackpad is discoverable. If the Trackpad has discoverable the green light will blink on and off. If it does not pair within 3 minutes you will have to press the power button again to re-initiate the pairing process. Once your Trackpad has paired, you can just leave it on and it will pair automatically when you reboot your Mac.
If you are having problems pairing, try turning off any other Bluetooth devices within 30 or so feet of your Mac mini. That includes other Computers, iPhones, iPads, etc. that may be in the area. Once your Trackpad has pairedwith your mini, you don't have to be concerned about other Bluetooth devices.
One other hint, I find that although the Wireless Trackpad does not eat batteries as fast as the Magic Mouse it still uses more than the Wireless Keyboard. It is a good idea to keep a supply of AA batteries around. I have used Apple's Rechargable batteries, but found they did not last that long before needing to be recharged. I have had the best battery life from Duracell Quantum batteries.