That's fairly straight forward
Code:
If ActiveCell.Column <> 2 Then
MsgBox "You're not in column B"
Exit Sub
End If
However, if your macro depends on the active cell being in a specific column, that indicates your code uses alot of select and activate. You might be well served spending a little time eliminating select from your code. You don't have to select cells/sheets in order to manipulate them...And add sheet names to each Range reference
Example.
Sheets("Sheet2").Select
Range("A1").Select
Selection.Copy
Sheets("Sheet1").Select
Range("B1").Select
Selection.PasteSpecial xlpastevalues
that could be changed to
Sheets("Sheet2").Range("A1").Copy
Sheets("Sheet1").Range("B1").PasteSpecial xlpastevalues
Basically anywhere you see Selection, replace that with whatever was previously selected.
You're code will be much faster, and not dependant on where the user puts the active cell.