Spreadsheets made for reading often put months across the top: one column for January, one for February, and so on. That layout is hard to analyze: a filter on "Q1" or a chart over time needs one row per department and month.
Unpivot turns the month columns into rows. Select the columns that identify a row (here Department) and choose Transform > Unpivot Columns > Unpivot Other Columns. You get three columns: Department, Attribute (the old column names, the months) and Value (the numbers).
Unpivot Other Columns is the safe choice: when July is added to the file next month, it's unpivoted too, because it's "other" than Department.