Installation of scenarios :
The installation is easy but it depends on the version of Civ2 you have : the original version or an add-on.
* With an add-on (Conflicts in Civilization, Fantastic Worlds, Multiplayer Gold, Test of Time), create a folder with the name of the scenario in the "Scenario" folder and extract there the files contained in the ZIP you downloaded. If you have downloaded sound files, you have to create a new folder called "SOUND" inside the folder of the scenario. So, to sum up, this is tree you're supposed to have for a scenario called <Potato> : Civ2\Scenario\Potato\Sound (files for the scenario are in the "Potato" folder and sound files, if they exist, in "Sound").
* With the original version, you cannot place scenarios' files in a folder, you have to place them in the root folder of Civ2. This is risky because you'll not be able to recover original files (especially graphics) unless you just copy the SCN file. To enjoy fully the scenario by copying all files, you can make a copy of all your Civ2 root folder before the installation, and replace them later if you need to.
* Caution ! With the Test of Time extension, you have to operate as if you had the original version of Civ2 (making a copy of the game), and you have to delete *.SPR and *IMP.BMP files before to unzip the scenario into the game.