What is the role of a "spotter" as noted in the biography, Marine Sniper?

A spotter is a sniper's partner, the second man in a two man team. The spotter is the half of the sniper team who discovers targets by using a powerful spotting scope or binoculars. The spotter can also, if required, direct the sniper's fire onto target, calling shots and suggesting sighting adjustments. The spotter also provides cover and security fire for the sniper. Often, a sniper team is composed of two snipers who take turns acting as spotter for their partner.