Might be a good idea to tell them what game you have FE1/ + expansion Pack/ Gold / FE2 - also what patch level are you playing at.
Downloadable Aircraft can be downloaded and flown by the player or AI no different to the stock A/C. They can also be added to campaigns, you can alter the flight models, skins, decals etc if you wanted to get into that.
The campaigns will be what you see in game, you can download other campaigns or make ones yourself - to do that you need to be able to be able to use Notepad.
You can switch all the on screen displays off (red/white icons) if you like, and get rid of the red planes on the map too - so you are dependent on the cockpit. Note the white icon is just a waypoint that you can see on the in game map.
Things to note on downloading aircraft - ones done for FE1 may need a bit of tweaking to get them working fully with FE2 for example. Also some will have cockpits, some may not, in that case you may wish to use a stock pits instead or you may not depending on how fussy you are - there will be a varying quality as they are created by hobbyists.