Selection.ParagraphFormat.Alignment = wdAlignParagraphLeft

' Also, wdAlignParagraphCenter, wdAlignParagraphRight, wdAlignParagraphFull

' You can check for alignment by checking the following property:
FontPos = Selection.Range.Paragraphs.Alignment

Where FontPos = 0 = wdAlignParagraphLeft
    FontPos = 1 = wdAlignParagraphCenter
    FontPos = 2 = wdAlignParagraphRight
    FontPos = 3 = wdAlignParagraphFull