The Sort object takes as many keys as you add: department ascending, then amount descending within each department. What makes it worth writing carefully is that a sort is one of the few operations in Excel that can corrupt data with no visible sign. Sort a range that's missing a column and the rows come apart — every department paired with the wrong customer, and nothing on screen looks wrong. Always sort the whole contiguous block, and tell it explicitly whether the first row is a header.

Sub SortByDeptThenAmount()
    Dim ws As Worksheet, rng As Range, lastRow As Long, lastCol As Long

    Set ws = ActiveSheet
    lastRow = ws.Cells(ws.Rows.Count, 1).End(xlUp).Row
    lastCol = ws.Cells(1, ws.Columns.Count).End(xlToLeft).Column

    ' The WHOLE block, every column — never one column on its own.
    Set rng = ws.Range(ws.Cells(1, 1), ws.Cells(lastRow, lastCol))

    With ws.Sort
        .SortFields.Clear                         ' old keys persist otherwise
        .SortFields.Add2 Key:=ws.Range("A2:A" & lastRow), _
                         Order:=xlAscending        ' department A-Z
        .SortFields.Add2 Key:=ws.Range("C2:C" & lastRow), _
                         Order:=xlDescending       ' then amount, largest first
        .SetRange rng
        .Header = xlYes                           ' NEVER leave this as xlGuess
        .Apply
    End With
End Sub

Paste into the Visual Basic Editor (Alt + F11 → Insert → Module), then run and save as macro-enabled (.xlsm).

• Group a transaction list by department, biggest amounts first.
• Order an aging report by days overdue within each customer.
• Put a list into a predictable order before a lookup or a subtotal.

A simulation — press Run to perform what the macro does to a sample workbook.

• Data → Sort dialog — Identical, by hand, with Add Level for each key. See the tip.
• SORT / SORTBY — Return a sorted copy and leave the source untouched, which removes the corruption risk entirely.