Get a book or take a class....The two "classic" books are

Wilderness Navigation: Finding Your Way Using Map, Compass, Altimeter & GPS, 3rd Edition (Mountaineers Outdoor Basics)

I have this and its ok...I found it to be a bit over thought and poorly organized as a book to learn from.  It has good information though


Staying Found: The Complete Map & Compass Book

which I have not read.  Both are available at the usual outlets

REI carries this one...I have no particular opinion but NOLS is probably a good source.

There are lots of others