# Use of Correlation score

How do we use a correlation score between two variables for analysing data?

I have a set of 20 features and need to predict 21st feature. Now is it necessary that correlation between any two features should be close to 1 ? If I have 2 features with corr score close to -1, then does this mean that they are contradicting and thereby decreasing the accuracy ?

So how do we use a correlation score in analysis ?