after Sub Macro1()
Type:

Dim x as Integer

That will define your variable for the system.

"May" wrote:

I've been trying to write a macro as below to commit above task, but errors
like "variable not defined" and "sub or function not defined" keep poping up.

Sub Macro1()
x = 3
Do While ActiveCell(x, 11).Value < ""
Cells(x, 10).Value = "PO#" + Cell(x, 1).Value + " " + Cell(x, 3).Value
x = x + 1
Loop

End Sub

Could you please help? I'm a beginner at the stage and so happy to find out
this wonderful community.