The maps are dynamically updated in real time, and can show:
- player locations
- grief prevention claims
- player homes
- custom markers
- the world border
These options can be set with the "layers" button in the upper left coner of the map.
Different dimensions as well as player icons can be found in the expanding panel on the right side of the map. Clicking on a player icon will center the map on that player. Clicking on your own icon is a great way to get oriented on the map.
Markers on the Dynmap can be purchased with diamonds by talking to an owner.
Full documentation can be found at http://dev.bukkit.org/bukkit-plugins/dynmap/