Under "Settings" you can click "Let students self-enroll by sharing with them a secret URL or code" to create a URL link that can be clicked on by students for them to self-enroll (this could be disabled by your institution).
Under "People" you can add with their email address, Login ID (username), or SIS ID (id number). Ensure that the people added are as students, it is the correct course and section.
For emails from Canvas, some students may have the notifications blocked from going to their email. To change this, while the student is logged in, they will go to "Account" on the side, then "Notifications". From there, there is a series of options to turn on and off for their email and push notifications. Students can add or edit contact information under "Settings" to add/change connected emails and phone numbers.