Building a Monthly Report from Spreadsheets

I am attempting to auto-generate 1 main, monthly report (spreadsheet) with data that is collected at 3 different satellite sites.  The majority of the data will come from 3 spreadsheets that are received each month.  Each of the 3 reports has the same format, but the values may be different.  

Currently, there is a lot of copying and pasting or re-typing of the same information.

There must be an easier way to get the values from the 3 reports, total them and insert that value to the main report.  Any help would be most appreciated.