Question on how to read a map

Hi There

Can someone tell me how to read info on maps, is there any videos about?

For example see the below screenshot from one of my recently mapped areas, what are the numbers across the bottom? are they height above sea level? Because I’m a little confused, we took off near the blue dot in the middle which is basically the lowest point of the mapped area and towards the blue area is about 30/40ft higher than where the blue dot is but none of the figures at the bottom make any sense?