Setup your Pi-hole:

• Connect the Raspberry Pi to your router
• Open the Ubiquiti router's dashboard in your browser, and open the Services tab
• Click on the Actions button, select View Leases
• Identify your Raspberry Pi in the list (look for the hostname of your Raspberry or its MAC address)
• Click the Map Static IP button, and give your Raspberry Pi a static IP address
• Click on the Details tab inside the open dialog, and enter the IP address you just chose into the "DNS 1" field. Feel free to add another DNS provider in the "DNS 2" field (this is used in case your Pi-Hole stops working).
• Restart the Raspberry Pi

You should now be able to login to your Pi-Hole web dashboard from your browser by going to http://<ip-address>/admin (click on login and enter your password to see everything).

• A more detailed installation guide by Vegard Vines Skjefstad
• https://pi-hole.net/2018/08/06/pi-hole-v4-0-released-with-ftldns-improved-blocking-modes-regex-docker-and-more/
• A graphic explanation of how DNS works