The scale tells us what a given measurement on the map equals in real-life distance.
The measurement on the map that we have is 2 inches, and it equals 8 miles:
2 in = 8 mi
This can also be written as 2/8. This fraction can be simplified, since both 2 and 8 are divisible by 2; it will simplify to 1/4. This is the same as 1 in = 4 mi.