This guide should help you get set up for solo play.
From the Main menu select Basic Game:
Now select Solo Game:
You’ll now have the option to change the opponents you are playing against. Tap the picture to cycle through them. The difficulties are Animal = easy, Human = medium and Robot = Hard. You can also set the position to empty to play against fewer opponents:
Once you select Play you will be able to select the size of stockpile you want everyone to play with. Select bigger stockpiles for longer games: