Inverse of the Standard Normal Cumulative Distribution

I am not well versed on statistics, I know enough to be harmful I guess. I am working on some statistical models for safety stock and came across a model that is using this function. In excel it is using the function NORMSINV() for a 98% service level. The results is 2.1. Can anyone tell me the difference between this and the standard deviation and why one would use this instead of the standard deviation? And please use crayons :cool: