Macro Autofill to last row - how?

Hi there

I know little about writing VBA code, and this is probably a no-brainer to you gurus out there, so please be gentle.

I have formulas in column C, D & E that I want to autofill down in a macro to the last row in column B. The number of rows in column B may vary every time I complete this sheet.

I have turned the "relative reference" button on while creating the macro, but I see in the VBA code that the cell number still appears ie. "A1:C66". How do I make it go to the bottom of column B despite how many rows there are?

This is what is appearing in the code:

Range("C2:E2").Select
Selection.AutoFill Destination:=ActiveCell.Range("A1:C66")
ActiveCell.Range("A1:C66").Select

Many many thanks
Lisa