There are two ways to start it.

First is easy/useless way, good for simple testing.
You put file with those linies in imerial_campaign folder.
And add at the end of file:

script
name_of_the_file.txt

And next time you start campaign it will be active (1 turn per year).
Unfortunetely it is useless since it prohibits you from saveing the games.


The other difficult/useful way consists of making this script a "show_me" sctipy that needs to be manually started every time you load a game.

For detailed instructions find old 4 turn per your script thread, when there is detail explanation how such scripts should be installed.