What does it mean when a map is drawn on a scale?

Depending on what the map is of scale is very important.

On a road map of a region you might read 1 inch equals 1 mile, this is so that the map can fit on the paper or computer monitor, actual size is not an option.

On a Map of the world the scale might be 1 inch to 1000 miles.

Or if if something is drawn to scale it means, that you have one part of the map in feet and the other side in meters.