I like to know if I can build deck on existing cement slab and pur boards directly on slab and how would I tie boards down to slab

This Wouldn't Be A Fun Job To Do , But You Can Use Sleepers, Basically Use 3/4 Or 2x4 Flatways On The Slab, Ramset Them In Place, And Deck Over Top Of Those, Now Attaching The Post Is A Different Problem, You'll Have To Use Some Metal Post Fasteners, Or Use A Method As You Would In Setting Some Post For Interior Stairs, Which Requires Boring A Hole In The Side Big Enough To Get A Wrench Into The Post And Drilling A Hole Into The Bottom Of The Post To Receive A Threaded Bolt That Is Anchored To The Slab.