Tag a classmate or the instructor on your post or a comment by clicking into the Tag Classmate section. Users that are tagged in a post or comment will receive an email notification.
To add a classmate or instructor you can either start typing the users name or click to view a list of classmates in your course and select one or more from the drop down.
When adding a comment, click on the tag icon to access the tag interface.
You can also tag users via the @Mentions feature. See the dedicated support document on @Mentions for more details.