Step 1: obtain one of the two templates below

Select a version you want to use and click on the file menu of Google Sheets and "Make a Copy"
Enter in the names of the characters you want to track

Go to Manual Template

Enter your guild name, adjust the filters, and it will automatically fill in the names.

Go to Guild Template

Step 2: sign up for Blizzard Dev portal

Go to https://develop.battle.net/ and click on Get Started Now

Step 3: Create a client

Just click the button!

Step 4: Fill out the form

Name your client, doesn't really matter what you choose. Leave the next box blank, you do not need any redirects.

Step 5: Reveal your secret

Click on SHOW SECRET You'll now see your secret

Step 5: Go to your sheet's Script Editor

Click on the Tools menu and select Script Editor

Step 6: Select Script

By default it should take you to wow_bfa.gs, but just in case.. make sure it's selected!

Step 7: Enter in your Client ID and Secret

Copy Paste the Client ID and Secret from the dev portal into your script, then save the script and return to your sheet.
IT CAN TAKE UP TO 10 MINUTES FOR YOUR DEV ACCOUNT CREDENTIALS TO START WORKING! (and sometimes longer, thanks blizz!)