ok.
You put graphene-mobile among the themes.
You don’t need to activate the theme, it just needs to be in place.
If you use the Graphene theme, then some graphene-mobile settings will still appear in the menu. Make sure you enter the API code you got, which will serve as your site’s login credentials when checking for updates to the mobile theme.
Then there are instructions about a plugin you need to use, which will automatically activate the mobile theme, on the fly, when your site is visited by a mobile.