dear all, can clear my doubts? thanks in advance.

1) how do you guys know the syntax of the statement? i know you guys
might say from experience. i really impressed by you guys knowledge on
the script.

2) what is this xl means? i notice xl tied with other verb like up,
filldefault, pastevalues,.....

lastrow = Range("C" & Rows.Count).End(xlUp).Row

3) how do i know when to use application?

totalsum = Application.WorksheetFunction.Sum(Range("e2:e" &
lastrow))

4) what is R1C1? i notice in macro use quite often. it means first row
first column? but not all the time i select that cell, right?

ActiveCell.FormulaR1C1 = "=TEXT(RC[-8]*100,""000000000000000"")"

thanks again.