This can be done by buying one on my Tindie store, or building one from parts.  Building a PD Buddy Sink involves standard surface mount assembly techniques (pick-and-place, reflow soldering).  Because of the USB connector, it's impossible to hand-solder the whole board, so buying one is the better option for most people.

First, put the PD Buddy Sink into configuration mode by holding the "Setup" button while plugging it into your computer.  In this mode, the Sink runs a command shell on a virtual serial port, allowing configuration of the device and real-time interaction with a power supply.  Documentation for the command shell can be found here.  Also see the firmware README for a more in-depth quick start guide, including information about how to install firmware updates.

Once the Sink is configured, using it is as simple as plugging it into a charger!  The "Status" LED blinks quickly to show that Power Delivery communications are going on.  If the charger can provide the configured power, the Sink makes it available on its output connector and blinks the LED slowly three times to indicate success.  If the charger doesn't offer the power you wanted, the Sink provides no power to your device to prevent damage, and turns the LED on solid to indicate failure.