The real words
The Power Query Editor
Power Query EditorA separate window, opened by Transform Data, where a table is shaped before it reaches the model. It edits the query, not the data: the source file is never changed.
Three parts to the window: Queries on the left, one per table; the data preview in the middle, showing the first rows only; and Applied Steps on the right.
Because the preview is a sample, a step can look correct on screen and fail on the full load.
Check against your class slides.