I have a small wedding cake and She would like to have fresh flowers (roses&greenery) cascading down square cake layers. Okay, so do I just insert them into the cake? Or I know they have something to insert flowers into the cake. What are they called?? Any options? Thank you

They are called cake spikes or posy picks. Or flower picks from a florist.
http://www.wilton.com/store/site/product.cfm?sku=205-8501
http://www.countrykitchensa.com/shop/cake-decorating-supplies/fresh-flower-cake-spikes/38/527/205/635827/
Or you could put straws (regular, bubble tea, or coffee stirers), as long as you plug the cake end with fondant or chocolate so the flower stem doesn't actually touch the cake. Each spike or straw you insert into the cake will make it a little less stable, so don't use too many.