How do I add my students? If you go to the People tab, and click the person+ icon near Add Students. The directory has all students and add, so start typing your students' names in. Also, if you have a list of email address, you can copy and paste it there (faster). By adding them manually, when students go to classroom.google.com, they'll see the class invitation and all they have to do is accept to join the class.
Another way is to create the class and give them the join code (in the Stream, under the name of the class), but this way requires more effort on the student's end.