What you are asking about is known as the U.S. Public Land System or the Rectangular Survey System. This is a method of land description used to describe over half the land in the United States. All angles in this system are set using true directions, i.e. true north, south, east or west.
From these starting points, the county is divided into 6-mile by 6-mile square townships. The townships are then further divided into 36 sections, each being one mile square and containing 640 acres. The sections are numbered beginning in the northeast corner and ending in the southeast, moving section by section from right to left then left to right in an alternating sequence. The sections are then divided into rectangular pieces maintaining a common square.
Now that I have you thoroughly confused, try this website to see if it helps explain what I just told you: http://www.ndsu.nodak.edu/instruct/isern/103/land.htm
I would recommend a google search using the query: U.S. Public Land System or Rectangular Survey System. You will get a number of urls which will provide graphics to help explain the system.
You can also pick up an Atlas and Plat Book of any county and in the front of the book will be an explanation of the land description system. The plat books are nice to determine who owns the property you are looking at. If you need access you now know who to call.