In many portals, the option to select students from right/left box and add/remove them exists. Another option is by clicking next to the name or SIS of the student.
This feature would make adding students to a course much easier for teachers without having to go looking for the login or SIS info. I know that SIS imports students to courses, but this feature is great for those teachers who need to create their club courses, for example.
I have attached samples from other platforms.