If you're going to use the Ultimate Remote to send keyboard and mouse commands to a computer, you will need a receiver device. It requires a TSOP38238 or TSOP38438 receiver chip and a Trinket M0 board. Bend the leads on the TSOP so that the pins will go into the RX pin (pin 3), the ground pin, and the 3v pin on the Trinket as shown in the image below.
Solder the leads in place and trim the excess. It will snap fit into the 3D printed case. There are two pins in the case that lineup with the mounting holes on the left end of the board. The lid will snap fit into place.
Here is a YouTube video that describes the entire process.