Report to sum all customer transactions by month

[vaskoco]

Hello everybody, completely new here. I tried searching for a solution many hours and just couldn't find any, so I decided to ask for help.

So I have monthly reports of my customers and I need to know how much every customer spent in the whole year.

I imagine that first I would need to create a new sheet and with some unknown formula to me to get all unique customer emails first.
And then next to it with another unknown formula to sum all the transactions from my original reports with customer email X.

Can you help me figuring out these two formulas?
Thanks in advance!

Administrative Note:
As per our Forum rules, we ask you provide a clear and descriptive thread title. As you are a new member with one post, I tried to do that for you based on your description.

[CRIMEDOG]

=Sumif(Report!C:C,B2,Report!D:D)
Where Report is the Tab that has the report - C:C is the column on the Report that has emails - B2 is the email you are checking - D:D is the column on the report that has Transactions

A lot of times I use countif to make sure the customer appears o the report (to avoid error)

[alansidman]

Have you looked at running a pivot table of your data. If you post a sample spreadsheet (see yellow banner above), I am sure we can help you with an easy to understand solution.