Usually check-in begins 2-4 hours before scheduled departure and closes 40-60 minutes before departure. However, at some airports international flight check-in begins 4 hours before scheduled departure and closes 1 hour before scheduled departure. Keep this in mind when planning your arrival to the airport. The flight ticket always displays the local departure and arrival time.
The passenger late for check-in is denied the boarding.
After passenger's check-in, the airline staff member check in your baggage and gives you the boarding pass with the number of your seat and baggage tag.
Then listen the announcement (or look the airport timetable) about boarding. You should then go to the gate indicated in your boarding pass or in airport timetable.