Tapping on the menu icon (at the bottom left of the game screen) opens a menu of quick in-game options.  From left to right:

• 'X' - hides  the menu
• 'Background' - toggles display of the guide image. Try turning it off for an extra challenge!
• 'Only show edge pieces' - select this option to hide all the unplaced pieces except edge and corner pieces. Tap it again to show all pieces.
• 'Shuffle pieces' - randomly moves around all the unplaced pieces.
• 'Place a piece' (Star icon) - prompts to automatically put one piece of the puzzle in its correct place, for a coin cost.
• 'Return to Map' - exits the current puzzle and returns to the Map View screen.