Importing a Google Classroom for use in Boom Learning allows your students to log in to Boom Learning with their Google accounts, and allows you to more easily assign decks to your students through Google Classrooms.
To import a Google Classroom, first make sure that all your students have been invited to your Google Classroom, and that they have accepted the invites. More information on inviting students to Google Classrooms can be found here.
Once you have all your students in your Google Classroom, navigate to your Classes tab and click the "Import from Google" button.
You will be prompted to sign in with Google. Sign in with the account associated with the Google Classroom you want to import, and you will be presented with a list of all Google Classrooms associated with that account.
Select the Google Classroom you want to import and click "Import Roster". All your students will be added to a new Classroom, and use Sign in with Google to access their accounts, as signified by this icon by their profile picture: