To register your attendance to a class at Hult, all you need is the myHult app, or to navigate to

From the bottom of the Dashboard page, you will find the "Attendance" link, click "View"

Once the professor has opened registration for a class (and before the check-in window closes), you'll see open class sessions at the top. From here, all you need to do is click "Check in"

Then you'll get a green "success bar" and be marked "Checked in"