Chooch got the 10,000 foot view of it covered. Here's a little more about each.
One thing - until you leave the controlled areas of immigration/customs - no cell phone or camera use is allowed.
First Immigration - make sure to have your form filled out completely. Otherwise a form checker will have you get out of line and go to a side area to complete it.
They will ask you your departure date and where you will be staying, not much more. The stub Chooch mentioned they will put in your passport - good place to keep it.
Soon as you leave Immigration, on way to baggage carrousel - there are restrooms and a Currency Exchange window.
The exchange rate there is significantly less than at cambios/banks elsewhere - so just get enough cash to hold you until town, if any at all.
The Transfer companies will all take $US. Many will stop once along the way for a break - food/drink/restroom - but they will also take $US, but you get better deal if you have $JA, but not so much better it is worth the airport exchange rate.
For Customs - there are 2 groups of lines. Red lines for people with something to declare - Green lines for people with nothing to declare.
The customs form is pretty good about telling you what you should declare - certain plants/fruits, meats, cigarettes above a certain number, gifts, tools, etc.
If you can travel without declarable items so you can go thru Green lines, it will save you some time.
Once you leave Customs you are no longer in Controlled area and can use cell/cameras again. You then come into the Ground Transportation area.
If you are staying at a big AI - they have areas for check-in to collect your bags and direct you to their buses.
The JUTA desk - for a cheap, but shared, transfer to your hotel is also here - to make arrangements with.
If you use one of these services, they will direct you to one exit (directly opposite the customs hallway) - that is a more controlled-area for arriving passengers with these type Transfers.
If you have made your own Transfer arrangements (like with Clive or many others mentioned here), you instead use the exit to the right (when leaving the customs hallway).
This area is open to the public and way more busy with ride providers of all kinds looking for business.
Tell whoever approaches you who you have arranged your Transfer with and they will hook you up with them.
If a friend is meeting you, this is where you would meet them.
It's not as bad as it sounds. I find if you don't worry about hurrying - and get into mindset that vacation has started so let's slow down - you start enjoying JA sooner.
