Studying MODX Revolution
MODX Revolution is a very easy Content Management System. Managing a site's content is simplicity itself, and the only difficulty you'll find in theming your sites is in deciding what complementary and contrasting colors to use.
Many commonly needed features and functions are provided by the repository of community-provided extras. The only hard part is deciding which one to use for any given feature.
When you want to dig deeper and create your own custom features and functions is where a more intensive study of how MODX works will bring its power and flexibility into play.