These and several other random number functions return a random value from a distribution. Ranuni from a uniform distribution on the interval from 0 to 1 and rannor from a normal distribution with a mean of 0 and standard deviation of 1.
Uses are many depending on your needs but basically revolve around a need for a random number. One example would be to add a value to set of data and use a specified subset of the data to select a random sample. For instance add a value x=ranuni (12345); to each record of a data set and then select x < .20 to get roughly a 20 percent random sample of the data.
