Powerquery function

Dear all,

I'm a bit stuck on the power query editor.

I have a very small dataset with the product name, the process step, the process cost, and the process date.

I want to create a report per product name, per process step, and per month the cost.

I thought the PQE editor could automate the report.

I thought group by account, sum on cost. But I cant create further analysis, like totals per month. What is my mistake?

Dummy data in attachment.

Greetings.