Click on the 'down arrow' icon to view the screenshot for each of the step.
Open your Classroom Dashboard for the subject and click class Settings.
Under General, refer the following:
Ensure Manage invite codes is Turned on.
You can copy the Invite link and forward the invite link to students.
Or, you can provide the Class code to student and students need to enter the class code when they join a classroom.
Join a class using the Invite link:
Students can click on the invite link and they will be directed to the preferred class
Join a class using a unique Class code: (Click on the 'down arrow' icon to view the screenshot for each of the step.)
Students will click on the "+" icon
Ensure the students sign in to Google Classroom using their .net account.
Enter the unique Class code and click Join