if you want to play a scenario from the forums:
Open the file. There should be another file inside it, 873e893489rny2348ofy24tf, kind of like that, just conjumbled numbers and letters (DONT COPY THE CONPRESSED FILE, THE FILE IN TRHE CONPRESSED FILE)
Put that boi into age of civlizations 2/map/earth/scenerios
2. How to copy a scenario already in the scenerios.
Go to age of civlizations 2/map/earth/scenerios
right click and go to "copy"
paste it in scenarios.
Now change the name to, if it were 1440, then 14402. make sure everything in the scenario folder that has "1440", the 1440 being switched to 14402.
Hope I helped you.