i am ready for the decking to go down. how deep do i screw the screws into the pt wood? do they go down flush or slightly below grade?

Slightly below would be fine. Flush would be alright too. This is really a matter of what you would like. There are lots of options available to make your deck look great. You can attach you decking with the screws that are available from your local building supply center or you can get creative. There are plugs available to hide the screws if you would like. There are also hidden fasteners available so you will never have to look at the screws. You can even get color match screws if you want.

Deckman