Check In and Check Out
Start and stop the clock on your working day, and what each press writes.
Two presses make a working day: one when you start and one when you finish. Everything else on your attendance record is calculated from the gap between them.
Open My Attendance and select Check In. The status changes from Not Checked In, the clock starts, and Remaining begins counting down against your scheduled hours.

Take breaks as you normally would. Time recorded as a break is held separately and does not count towards Net Working Time, which is why the two figures differ by the end of the day.
Select Check Out when you finish. The button in the band changes to Check Out for as long as you are checked in.
Once you check out, the day stops being live and becomes a row in your attendance records, with the status Worklink worked out from your shift.
If you forget
You cannot check in for a day that has passed, and you cannot edit your own record. Both are deliberate: an attendance record that its owner could rewrite would not be worth keeping.
The route back is a regularization, which puts the correction in front of your manager instead.