Auto-play speeds up some games by quickly moving available cards into foundations.
Tap the Auto toolbar button to use it. If the button isn't available, auto-play can't be used with the current game.
Auto-play is not smart, it's only for convenience. It won't make moves within tableau, reserve or waste piles.
Use Auto-play wisely and keep an eye on what it's doing. The choices it makes can lose an otherwise winnable game.
Double-tapping a card will auto-play that individual card. This is the best way to use auto-play — you get the speed benefit while making the decisions yourself.