Simple listing of Get-Date -format so you can see what each looks like:

Get-Date -f d 9/23/2015
Get-Date -f f Wednesday, September 23, 2015 9:24 AM
Get-Date -f g 9/23/2015 9:24
Get-Date -f m 23-Sep
Get-Date -f o 2015-09-23T09:24:03.2463374-05:00
Get-Date -f r Wed, 23 Sep 2015 09:24:03 GMT
Get-Date -f s 2015-09-23T09:24:03
Get-Date -f t 9:24 AM
Get-Date -f u 2015-09-23 09:24:03Z
Get-Date -f y September, 2015