Once a Class In-charge starts a lecture using Acadly, every student is notified that the lecture has begun. The students can then "Check In" to the lecture. There are two ways to record attendance:
Manual: Once a student checks in to a lecture, their name shows up on the Attendance tab of the Lecture page. The Class In-charge can then do a manual roll call during the lecture to see which of the checked in students are actually present at the venue. Using the same list, the Class In-charge can mark the students as "Present". Acadly works on the idea of capturing the intent of a student to attend a lecture, hence allows the students to check-in to a class even if they are not physically present at the venue.
Automatic: Everything you need to know about automatic attendance is in a separate help section titled "Attendance". Please do go through it. You can also read about automatic (one-tap) attendance here.