I urgently need to know if the word choice and tenses are correct. Thank you.

1) Enter the airport and check your flight number and the boarding time of your flight on the departures board.
2) Before going to the check-in desk make sure your baggage doesn't exceed 20 kilos. You pay for excess baggage.
3) Put your luggage on the conveyor belt (carousel) for it to be weighed.
4) The check-in clerk will check your passport and ticket and will give you a boarding card with your seat number and the boarding time on it.
5) Then go through security and show your passport.Put your hand luggage and any metal object in a basket for them (?) to be scanned.
6) Then walk through the metal detector. If it alerts (I don't know the word), a security officer (?) will check your body for metal.
7) Go into the departures lounge where you can buy things in the duty-free.
About half an hour before take-off go to your gate number and wait for your flight to be announced.

I already checked these sentences once, and Dr Russ has checked them (see post below).

What do you NOT understand?