A "component" is a large block of page functionality. In this case, it refers to:
- Top Level View (how the top level of the site looks)
- Folder View (how items listed in a folder look)
- Message View (how messages look listed in a discussion
- Toolbar (how the list of buttons or links looks at the bottom of the page
Most Components have an extensive page of settings you can reach from the Component Manager pulldown menu once you have it enabled.
The Component Manager allows for a lot of customization "bang" for very little effort. Next time, Folder and User Items.