Inserting rows based on cell

Can anyone explain to me how this code works? I found it in an article.

Sub CopyData()
    Dim xRow As Long
    Dim VInSertNum As Variant
    xRow = 1
    Application.ScreenUpdating = False
    Do While (Cells(xRow, "A") <> "")
        VInSertNum = Cells(xRow, "D")
        If ((VInSertNum > 1) And IsNumeric(VInSertNum)) Then
           Range(Cells(xRow, "A"), Cells(xRow, "D")).Copy
           Range(Cells(xRow + 1, "A"), Cells(xRow + VInSertNum - 1, "D")).Select
           Selection.Insert Shift:=xlDown
           xRow = xRow + VInSertNum - 1
        End If
        xRow = xRow + 1
    Loop
    Application.ScreenUpdating = False
End Sub

Does it copy and paste rows from columns A to C based on value in cell D or does it duplicate it another way? I want something like this except I want to insert rows and only copy columns A and B. But if I don't know how to change this code so that column C also shifts down.

An adaptation like this would insert an entire row and then paste the values from A:B:

If ((VInSertNum > 1) And IsNumeric(VInSertNum)) Then
    Range(Cells(xRow + 1, "A"), Cells(xRow + VInSertNum - 1, "B")).Select
    Selection.EntireRow.Insert Shift:=xlDown
    Range(Cells(xRow, "A"), Cells(xRow, "B")).Copy Range(Cells(xRow + 1, "A"), Cells(xRow + VInSertNum - 1, "B"))
    xRow = xRow + VInSertNum - 1
End If

Something like this may be what you want:

Sub CopyDataAB()
    Dim xRow As Long
    Dim VInSertNum As Variant
    xRow = 1
    Do While (Cells(xRow, "A") <> "")
        VInSertNum = Cells(xRow, "D")
    If ((VInSertNum > 1) And IsNumeric(VInSertNum)) Then
Cells(xRow + 1, "A").Resize(VInSertNum - 1, 2).EntireRow.Insert
Cells(xRow + 1, "A").Resize(VInSertNum - 1, 2).Value = _
        Cells(xRow, "A").Resize(1, 2).Value
           xRow = xRow + VInSertNum - 1
    End If
            xRow = xRow + 1
    Loop
    
End Sub

*it relies on the number of rows to be entered in column D