Nodelets are small boxes which display information or provide an interface to some function of the site. There are many nodelets to choose from. Some are available only to certain orders of monks. You can add and remove nodelets to/from your default page display, and control the order in which they are presented; do this on your Nodelet Settings page. See How do I change my preferences? for details.
Now go check out The Available PerlMonks Nodelets.
(Note: The nodelets available only to gods are not documented here.)
The links below are for the sake of old nodes which linked here for nodelet documentation. Move along, move along...