The first thing you want to do is log in to your Google account from your default browser. Google Docs Building Blocks works in most web browsers. The only exception is that Building Blocks doesn’t seem to be available on the mobile version of Google Docs. Maybe Google will roll out the feature to the mobile version at some point. In the meantime, stick with your desktop browser.
Also: Are your Google Docs safe from AI training?
Once you’ve opened Google Docs or Google Drive, create a new Google Document.