If you create a class by importing from Google Classroom, CommonLit automatically creates your students' accounts. You do not need to manually invite them to join your class too.
Students should log in using Google Single Sign On by clicking the Log in with Google option on the CommonLit login page:
The first time they log in, they may be prompted to select a grade level if your class has multiple grade levels. Students will then be asked to connect their CommonLit account to Google Classroom.