Excel Applying Code to a Column

[sk1994]

Hello,

I'm teaching myself VBA and ran into an problem I cannot solve.

I'd like to click the button I made so that it automatically knows what column to refer to when performing the macro.
The macro currently works if I select the cell then press the button. But I would like the button to automatically know which column of cells to perform the function on.

Here is my code:

Sub Sheet3Grades()

Dim score As Integer

score = ActiveCell.Value

If score >= 100 And score <= 199 Then
ActiveCell(1, 2).Value = "F"
ActiveCell(1, 2).Interior.Color = RGB(255, 0, 0)

ElseIf score >= 200 And score <= 299 Then

ActiveCell(1, 2).Value = "D"
ActiveCell(1, 2).Interior.Color = RGB(255, 178, 229)

ElseIf score >= 300 And score <= 499 Then

ActiveCell(1, 2).Value = "C"
ActiveCell(1, 2).Interior.Color = RGB(204, 204, 255)

ElseIf score >= 500 And score <= 599 Then
ActiveCell(1, 2).Value = "B"
ActiveCell(1, 2).Interior.Color = RGB(153, 255, 255)

ElseIf score >= 600 And score <= 699 Then

ActiveCell(1, 2).Value = "A"
ActiveCell(1, 2).Interior.Color = RGB(0, 255, 0)

ElseIf score >= 700 And score <= 799 Then

ActiveCell(1, 2).Value = "A+"
ActiveCell(1, 2).Interior.Color = RGB(255, 255, 0)

End If

End Sub