Information automatically updated

Hi,

So I am creating a file for my boss on excel 2016 that I want to automatically update information from one table to the other without me having to re put it in. On one workbook, I have all of the agent sales for the year separated out by month and transactions within that month. I want to have another workbook of just numbers that takes the sales from those certain months to automatically add up after filling it in on the other workbook.
I can't seem to get a formula or link workbooks together to do it the way I want. Any help?