Sitefinity Script Manager Documentation

Could someone please point me to documentation on how Sitefinity's script manager(s) work in Sitefinity 5.0 SP1? I couldn't find anything substantive in the official documentation. What's the relationship between adding a radscriptmanager and the automatic stuff that happens even in a custom template? I have figured out how to turn the script business off under the page settings section and use a different theme for the css, but I'm in the dark as to how I'm supposed to use this system effectively.