Question: I want to set "Formula" to all cells in certain column **whatever the number of rows was**.

**But i don't want to set this function to first cell "Header" of this column**.

How do i make it ?.

Answer: 
If your header is in cell A1 and your formulas need to start in A2 and go to the end, **start by selecting A2, press (and release) "End" then press "Shift+Down Arrow"**. Now everything from A2 to the end is selected and you can paste your formula. If you have no data in A2-A65535, you will select the entire range. If you have data, this will only select to the end of the list of data.
for example if you want to apply SIN(x) on a set of data in a row, in a vacant cell type:
=SIN("click on the first cell of the row")
then press "enter"
then grab the handle of this cell and draw it up to the last cell.
now you have a set of data in a row each cell of which is has the value of the SIN(the original cell)