Don't feel bad -- my DH regularly has trouble getting out of MCO. (He's a wee bit directionally impaired, poor thing.) The answer to your initial question is no, they do not all leave from the same car park, because there are two rental car parks, the one on the A Side, and the one on the B Side.
When you leave the car park (either one of them) you will be directed to exit the carpark ramp to the left (this is because the ring road around the airport is all one-way traffic moving counterclockwise around the airport itself.) The tricky part here is that there are fairly quick lane changes, and that can be a bit intimidating when you are still getting used to driving on the "wrong side" (or even to driving an unfamiliar car.) If you miss getting in the proper lane the first time, don't sweat it -- just keep the buildings close on your left until you get your bearings. The road will take you round the terminals in a circle, and eventually you will be able to get into proper position to exit on the correct road: which is the South Exit.
The internal road signage that you need to pay attention to at MCO is overhead signage, and no matter how many times you seem to be circling round the terminals, eventually you will find the proper road. What you are aiming for is this one (note the color):
What can sometimes complicate finding this exit is that you will also see smaller overhead signs at other points in the ring road around the airport that say
South Exit but do not seem to be exit ramps: they are not exit ramps. They are leading signs that are there to get you into the proper lane position to be ready to exit when you finally see this LARGE orange South Exit sign. This can be really confusing if you happen to come out of the A side garage, because if memory serves, the first South Exit sign there is actually on the lefthand side (which keeps you from exiting the airport in the wrong place), but then, once past it, you have to move over to the righthand side in order to line yourself up for the actual
South Exit ramp, which is on the righthand side of the ring road.
Going this way there are tolls on the road; be sure to buy a drink or something in the airport terminal and get a bit of change so that you have $3 or so in US coins for the tollgates, because not all of them have an attendant. In those cases, you need to toss the coins into the collection basket in order to operate the gate. (There are some gates that do have attendants, and they will be able to take US notes with no problem, but you will need some coins as well.)
I do have to say that the rental car exit (and also when returning the car) is VERY poorly designed. I never look forward to leaving from--or returning the car to--the airport.
