About student attendance
When you start a session, you are shown the expected students for the session and you can deselect any students that won't actually be present for the class. You can sort the list of students by Name and Status. When you sort by the student's name, this is only for the student's first name.
If a student is shown as not available because they're in another session, but you have the student in front of you, you need to ask the teacher who has the student in a session to remove them from their session before you can add them to yours.
You can also set when you expect the session to end.