Adding to the others. Spend an hour or two to get somewhat familiar with the
R1C1 notation style, it is very essential for VBA programming in Excel. For
example, this line

ActiveCell.FormulaR1C1 = "=SUM(R1C:R[-1]C)"

will enter a sum formula, summing from row 1 same column to the cell just
above the formula cell, no matter which cell that is active. To do a thing
like this in A1 style you must first know the the column letter of the cell,
row number, ...

HTH. Best wishes Harald