Launch the game using the normal Kingdoms shortcut, which should bring you to a launcher window with news and other information.- In the lower right corner there's a button which reads "Play". Click that and you'll get a drop-down menu with several mod choices.
- Select "Stainless Steel" from the menu and off you go.
In other words something like this, except you select "Stainless Steel":
Pic shamelessly borrowed from
here