Monklets are predefined code snippets that allow you to bring in other module content (sermons, events, etc.) into your pages. There are a few monklets that have been created that are placed in sections that you can assign to various sections on your site.
You can use a monklet inside a section by placing your cursor in the content area, selecting Insert > Insert Monklet > "Desired Monklet".
Monklets allow inline parameters to be passed to define items from a specific group, category, etc. http://help.monkcms.com/article/using-monklets/ provides details on using these parameters.