Nothing like leaving it till the last minute...!
As an ex check-in agent for well known unpopular ground handling company I hope I can help a little in this respect. Essentially you'll start you're shift on a checkin desk. It varies between airlines but you'll have a computer through which you check-in passengers. It's like filling in a register I guess. You can bring up a seat map of the aircraft on the screen and you assign the seats from there, trying to keep everone happy, keeping families and couples sat with each other and window seats etc.
You need to make sure they have their correct tickets, although many scheduled carriers are using electronic ticketing, which, as long as you IDENTIFY the passenger correctly(!) can save a lot of paperwork. The agent must ensure that passports are in order, that Visa requirements are satisfied etc. Information on this can be brought up in some computers or in the 'TIM', a big book that says who can and can't go where with which visas... makes a gripping read... However, if you did send someone somewhere and they were denied access due to a problem you should have picked up, the company will be fined. And you'll know about it...
Baggage must be weighed and ticketed then sent down the belt. Excess baggage will need to be paid for via the ticket desk. Some airlines allocate a share of the charges taken to either the whole checkin team, or those that have charged for excess individually. I never had this opportunity with 'my airline' so nobody that I checked in ever got charged excess! Unless I felt they deserved it.... and some do! If the passenger is not happy about paying £4.00 a kilo for their 3rd suitcase (and I've yet to find one that is) it'll be up to you to diffuse the situation, maybe coming to a compromise by rounding down from say 24 to 20 kilos? There's always the old, 'ok well you don't pay, you don't fly...' you have them by the bollards...and money will suddenly appear from the person who previously couldn't afford blah blah blah....
Some rows cannot have infants sat in them due to lack of oxygen facility, so this must be prepared for by 'setting up' the flight in the computer before checkin opens. Seats can be 'blocked' for wheelchair passengers etc. This will normally be done by a checkin supervisor or equivalent, but an agent might do well to learn this sort of thing if they wish to progress in the company!
Obviously there are the mandatory security questions you are required to ask;
'Has anyone asked you to carry anything onto the flight for them?'
'Could your bags have been interfered with since you packed them?'
'Do you have any sharp or pointed items about your person or in your hand luggage?' Words to that effect, I forget it's been so long! Any 'jokey' responses to these questions normally result in the checkin agent calling the police...
Check-in agents also board the flights from the gate. You'll start the (often long) walk to a deserted gate room a suitable amount of time before the flight and ensure that the screens that show to the passengers are changed at the right time, say 1 hour before departure. Activity here ranges from setting up the boarding process to seeing who can slide furthest on their chairs... One gate I used a lot had a hot drink machine in, and the engineer told someone a code to get drinks out of it for free! It genuinely worked too! Hot chocolate to order!
The agent will liase with the despatcher as to when the crew on the aircraft are ready to accept passengers, then you'll do your announcement (which is AWFUL the first few times) and board the aircraft normally from the rear first. You'll need to arrange for calls to be put out for late passengers and then make sure that everyone is indeed on board, that someone hasn't slipped past you to go to the toilet. Then it's back up to check-in, maybe via the canteen.
We have a ticket desk but I work for a Ground Handling Agent (Servisair) so our ticket desk is responsible for several airlines mainly scheduled airlines. The airlines themselves use different computer systems for check-in and reservations etc. A ticket agent will need to learn all these systems which is no mean feat! Rebooking onto another flight if there is disruption due to weather or technical problems, possibly booking hotel accomodation for passengers or distributing refreshment vouchers can all be done by the ticket desk. This is different from somone working in a call centre handling reservations, our Ticket Desk is on the airport floor, Zone F of Gatwick South if you were passing anytime. This is where passengers will come to pay that excess we were talking about, and ticket desk staff often have to deal with difficult passengers. There is a large amount of responsibility as far as money handling is concerned. I've seen some large sums at the end of a busy day!
I know nothing about retail staff in the airport. If they are 'landside,' I'm sure it's the same as working in the high street. If you're 'airside,' you'll have to go through security but again I guess it's fairly similar. Possibly handling different currencies I don't know? All (good) airport staff have a sixth sense for security though and this would set someone apart from the high street. Unattended bags, shifty looking people tend to become slightly higher priorities especially where flights are concerned. I've had a phone call on checkin from a girl that worked for a completely different company advising me of a possible drunk passenger that was on his way over to me to checkin. He had to ask her directions, then fell over in front of her. He didn't fly that night.
Again, I know little of security as a job role. Not sure if it's as exciting as it sounds. There are lots of security posts that require constant supervision day and night, and they are often on their own. They obviously have the responsibilites of all the passengers that are travelling day to day and I'm sure the resposibility is not easy. It would probably be best to contact the BAA direct about it. Most airport workers are a pretty helpful bunch.
I've rattled on quite a bit but hopefully the above is helpful....
PM me if you want me to expand on anything...
All the best
Andy