The minimap is a map of the world you're in that you can bring up while in game. It shows where the spawn teleporters are, where you are in the world, and small icons for any self-protecting items that you've placed.
Depending on your perception skill level, it can also show what areas have been explored, as well as the titles of plaques and landmarks. It also displays important information like the percentage of world exploration, percentage of acidity, how many machine parts have been found, as well as options for zooming in and bookmarking your favorite worlds.
How to Use
You can bring up the minimap by tapping the map button (lower right on iPad, lower left on iPod) or, if you're on a desktop computer, by just hitting the M key.
There are four buttons to the right of the map, but only two of them function.
The first button looks like a magnifying glass; hitting this will cycle your view through whatever zoom capabilities you have (based on your perception skill level).
The next one down looks like a bullseye and is just there to look pretty.
The third button looks like a camera and will take you to a dialog box that makes you think you're taking a screenshot of your screen. At the time of this writing (February 2016), however, this process is a lie, and no screenshot is saved to your device.
The final button has a star on it, and clicking it will turn the star yellow and bookmark the world. You can view your bookmarked worlds from the world teleporter panel under the "personal" section.
As of February 2016, the minimap on v3 (PC/Steam users) lacks many of the functions listed above.