Think of these as analogous to sections of an orange. 0 degrees latitude is the equator. Longitude 0, the Prime Meridian, passes through Greenwich, England. To the west of Greenwich, lines of longitude go to 180W, and to the east of Greenwich they go to 180E, for a total of 360 degrees. In recording the location of a point on the Earth's surface, it is necessary to specify north or south latitude and east or west longitude.
Longitudinal distance decreases toward the poles.
The approximate distance between any 2 points on the surface of the Earth is an angular distance. The 2 in the formula is squared, not times 2. You will get more practice with this formula in lab. The figures below show the world mapped using 4 different projections. Each projection has certain properties that make it more or less useful for certain applications.