Statistics is a part of mathematics. We collect data items or a sample of a population related to a particular characteristic. Then we find various quantities like mean, median, standard variance etc. and analyze the data by using the statistics.
Statistics gives us a way of characterizing a given population based on samples and then predicting the values of desired characteristics of some other samples.
The characterization of given data is useful in presenting data, knowing the sample size needed for a given population. It is also useful in knowing error margins in predictions, or , the confidence levels in making statements about populations.