Autofill based on selected cell

I'm pretty new to programming and VB in general. I've searched and cannot find this anywhere so I apologies if this has already been asked here. I’m writing a script that will, given the column names be able to complete a series of things with two excel files and eventually run some regressions regardless of coordinates as those are likely to change from file to file. I’ve been naming different columns as Ranges and been doing fine until now. I’m trying to auto fill a formula to the bottom of the file. Everything I’ve seen for this has exact coordinates. Such as

Selection.AutoFill Destination:=Range("F1:F" & Range("A" & Rows.Count).End(xlUp).Row)

But I don’t have exact coordinates. Ideas anyone? Thank you for your time.