The add-on needs to be opened from inside Google Docs,.

You can watch this video or keep reading:

The first step is to open a Google Doc.

Next:

Here's what that looks like:

The first time you open Kaizena, you'll see a message saying "A script attached to this document needs your permission to run." - click "Continue."

You'll see a popup asking you to select your account: if you have multiple Google accounts, make sure to select the account you use for school. Kaizena will ask for permissions - click "Allow":

Next, you're ready to sign in for the first time!