ref is a required argument that is the reference to a range.
ref_style (optional) is determines whether ref is in A1 style (columns are named with letters and rows with numbers) or R1C1 style (both columns and rows are named with numbers). If ref_style is True or missing, ref is in A1 style.
equals 100 if cell A1 contains C108 as a reference and cell C108 contains a value of 100.
=SUM(INDIRECT("a1:" & ADDRESS(1,3)))
totals the cells in the area of A1 up to the cell. The cell address is defined by row 1 and column 3. Therefore, area A1:C1 is totaled.
Parent topic: Spreadsheet functions