Returns or sets the distance (in points) between the left edge of the text frame and the left edge of the inscribed rectangle of the shape that contains the text. Read/write Single.
Example
This example adds a rectangle to myDocument, adds text to the rectangle, and then sets the margins for the text frame.
Set myDocument = Worksheets(1)
With myDocument.Shapes.AddShape(msoShapeRectangle, _
0, 0, 250, 140).TextFrame
.AutoMargins = False
.Characters.Text = "Here is some test text"
.MarginBottom = 0
.MarginLeft = 100
.MarginRight = 0
.MarginTop = 20
End With