If you type wdAlignParagraphLeft in the Search drop down box (next to the binoculars), then do the search (Click on the binoculars), you will see that it's a member of the
WdParagraphAlignment class. You will also see that it's a constant that is equal to 0. The other constants of the WdParagraphAlignment class are also listed. You'll see that wdAlignParagraphCenter = 1, wdAlignParagraphDistribute = 4, etc...
So,
Selection.ParagraphFormat.Alignment = wdAlignParagraphLeft
is the sames as
Selection.ParagraphFormat.Alignment = 0