What is the spotter's job? How does he help?
The spotter describes the target and identifies it within the scene (using a higher-resolution scope than the rifle is equipped with). The spotter also describes wind conditions, estimates or measures range, and otherwise assists the sniper in making the shot. If the sniper misses, the spotter identifies the hit location so that the sniper can correct for it in a following shot. Although there are many solitary snipers, there are also a lot of 2-man sniper teams. The comedic soccer sniper series has such a two man team, the spotter and the sniper, working together.
https://www.youtube.com/watch?v=S0d9V7wdocA
He had a spotter of extreme skill...
“What is the spotter’s job? How does he help?”
He must first determine range, then factor in wind conditions that are not uniform over that distance, factor air temp, air humidity, difference in elevation to the target, barometric pressure, oddly the rotation of the earth etc. He gives the firing solution to the shooter. Both spotter and shooter are extremely skilled. It really is rocket science.
The both deserve free beer!