How to use variables in a VBA code using the sumif function - excel

Question

I download a data set that always has a different number of rows. I store two columns as variables, the imports and the months. Then I need to run a Sumif formula that sums the value of imports by the months. I am writing a Sumif formula that uses the two variables and references the cell to its left.
The cells however vary in location based on the changing size of the data set. So I write a code to select the last active cell on a column and select the cell 3 rows down.
When writing the formula with the variables and the cell its giving me an error. Please help sorry for any typos fist time doing this.
I select all the active cells in range D and store them as months, I do the same for the imports. Then using range I find the last active cell on column M, and use select the cell 3 rows down, where I wish to write my formula.
Please see my codes to see what am I doing wrong, I am a novice coder.
Sub Importaciones()
'
' Importaciones Macro
'
Dim LastRow As Long
LastRow = Range("L" & Rows.Count).End(xlUp).Row
Dim Months As Long
Months = Range("D2", Range("D2").End(xlDown)).Select
Dim Imports As Long
Imports = Range("M2", Range("M2").End(xlDown)).Select
Dim LastRowM As Long
LastRowM = Range("M" & Rows.Count).End(xlUp).Row
Range("M" & LastRowM + 3).Formula = "=sumif(" & Months & ", " &
Range("L" & LastRow + 3) & ", " & Imports & ")"
End Sub
For the formula to work and the sum of the month that I choose comes up

Answer 1

As per all the comments:
Sub Importaciones()
With Worksheets("Sheet1") 'Change to your sheet
Dim LastRow As Long
LastRow = .Range("L" & .Rows.Count).End(xlUp).Row
Dim Months As Range
Set Months = .Range("D2", .Range("D2").End(xlDown))
Dim Imports As Range
Set Imports = .Range("M2", .Range("M2").End(xlDown))
Dim LastRowM As Long
LastRowM = .Range("M" & .Rows.Count).End(xlUp).Row
.Range("M" & LastRowM + 3).Formula = "=sumif(" & Months.Address(0, 0) & ", " & .Range("L" & LastRow + 3).Address(0, 0) & ", " & Imports.Address(0, 0) & ")"
End With
End Sub