Creating relationship between multiple tables from different months.

Hi All, 

I have just started using Power BI and I have a question about relationships between tables. I have multiple revenue reports from different months, and each report has identical column headings. How can I tell the program that these tables are related so I can show revenue of products over time? Do I have to aggregate all of the data into one table before bringing the data into BI, or is there a way in the program to get it to display revenue as a function time from monthly reports?

Thank you!