How do you use longitude and latitude to locate exact locations on the earth?

This system of using longitude and latitude to find exact locations on the earth is called the geographic coordinate system.

Latitude is the angle from a point on the Earth's surface and the equatorial plane measured from the center of the sphere. Lines joining points of the same latitude are called parallels, which trace concentric circles on the surface of the Earth, parallel to the equator. The north pole is 90° N; the south pole is 90° S. The 0° parallel of latitude is designated the equator. The equator is the fundamental plane of all geographic coordinate systems. The equator divides the globe into Northern and Southern Hemispheres.

Longitude is the angle east or west of a reference meridian between the two geographical poles to another meridian that passes through an arbitrary point. All meridians are halves of great circles and are not parallel. They converge at the north and south poles.

By combining these two angles, the horizontal position of any location on Earth can be specified.