I am absolutely new to this space and seeking suggestions<p>Problem:<p>I have an array with 12 values, one value for each month( think of these values as spending of a user each month ).<p>What I want to do is given any two dates, want to know his spending between these two dates<p>For this I need to learn how to fit models.<p>Please suggest me where to start resources, I will follow it from there<p>Thank you