Hi Pete, this is Dave, the developer.There's an extensive tutorial that shows how to play. The tutorial starts automatically on first launch, or you can rewatch the tutorial by going to Settings|Tutorial. Tap the arrow buttons at the bottom of the tutorial screen to move through each step.The quick explanation is this: There are core tiles (the red ones with two numbers), and outer tiles (the gray ones with a single number that surround the core tiles). The top number on a core tile shows the sum of the numbers on the outer tiles. The bottom number is the sum you need. You move tiles around by tapping any two outer tiles on the board, causing them to swap places. The sums for each core tile will then recalculate and any that now match your target sum will turn green indicating it's correct. Repeat until all of the core tiles are green. The first core tile is the easiest, but it gets harder for each of the remaining ones. Sometimes you'll have to break a core tile in order to solve the whole board. Every board has a solution. The small/easy boards can usually be solved in 1-10 minutes. The larger/harder boards can take longer.I hope you revisit the game and give it another shot. If there's a way I can make it easier to understand how to play, please let me know. I'd really like to earn your 5 stars. :)Thanks!