Cells(row, column) refers to one cell by numbers, which is what loops need. Cells with no arguments is every cell on the sheet.

Code

Cells(i, 2).Value

• In a loop

  Cells(i, 2).Value → Column B of row i

  Inside a For loop.

• Column letter

  Cells(1, "C") → A column letter works too

  Mixed forms.

• Build a range

  Range(Cells(2, 1), Cells(lastRow, 3)) → A block built from numbers

  Computed ranges.

• Cells(Rows.Count, 1).End(xlUp).Row is the last used row of column A.
• Cells.ClearContents clears the whole sheet.
• Qualify with a sheet in both Range and Cells when building a range from them.

• Range(Cells(...), Cells(...)) with the Cells on a different sheet than the Range errors.
• Cells(0, 1) errors; rows and columns start at 1.