Making new scenario folder
All scenario folders are located in \data\scenarios\ folder.
First thing that must be done is to secure game files from any changes made during the modding process.
The best way to do this is to copy one of the scenario folders and paste it in the \data\scenarios\ folder, after that please change the name of the folder to anything that fits the scenario idea (example: My_Scenario).
Now the game still doesn't see that new scenario folder. It is because settings are pointing into another folder. To make the new scenario active go the \data\scenarios\My_Scenario folder and open Info.ini file.
In the first line of the file insert (under Name) name of the scenario which is displayed in the scenario screen. At the bottom of the file (under ScenarioName) entry must be identical to the name of scenario folder, which in this case is My_Scenario.
I think that all other entries are pretty self explainable so if something is not clear, please ask.