Power Query is the data-shaping tool built into Excel (Data > Get Data) and Power BI. You point it at a file (Data > Get Data in Excel, or New Source inside the editor), then clean it with buttons instead of formulas. Every click is recorded as a step in Applied Steps on the right, and the steps run again, in order, whenever the data refreshes. That's the point: clean a monthly export once, and next month the same steps clean the new file.
When you open a CSV file, Power Query adds three steps for you: Source reads the file, Promoted Headers turns the first row into column names, and Changed Type guesses a type for each column. Select any step to see the data as it was at that point.
The formula bar shows each step in M, Power Query's language. You don't need to write M yet; the buttons write it for you.