Two directions, one place
Latitude tells you how far north or south a place lies from the equator. Longitude tells you how far east or west it lies from a reference meridian. Both are measured in degrees.
One number narrows the search to a band around Earth. The other helps choose a position around that band.
Begin with the equator
NOAA describes latitude lines as parallels: they run east–west but measure a north–south position. The equator is 0° latitude. The poles are 90° north and 90° south.
Longitude uses meridians running between the poles. A label such as 30° E means thirty degrees east of the zero meridian; 30° W points the other way. Our prime meridian reading explains why the historic Greenwich line and modern satellite reference are not exactly the same.
Read a labelled pair
Take this made-up example: 20° N, 30° E. Here we have written latitude first. It describes a place north of the equator and east of the zero meridian.
Now change the second label to 30° W. The latitude stays the same, but the place moves to the other side of the zero meridian. Keeping the numbers while losing N, S, E or W can change the location completely.
Zero still means something
A latitude of 0° puts a position on the equator; it does not mean the measurement is missing. A longitude of 0° uses the reference meridian.
Coordinates answer “where?”. To turn a measured gap on a paper map into a ground distance, continue with map scale. The four steps are gathered in Read a world map.