This example adds a slide to the active presentation and then adds text to both the title (which is the first placeholder on the slide) and the subtitle.
Set myDocument = ActivePresentation.Slides(1)
With ActivePresentation.Slides _
.Add(1, ppLayoutTitle).Shapes.Placeholders
.Item(1).TextFrame.TextRange.Text = "This is the title text"
.Item(2).TextFrame.TextRange.Text = "This is subtitle text"
End With