

Don't despair if you find it hard to keep an entire game in your head. If you hold down this new button, you'll get to see where all the pieces are. It will be marked where in the game you've peeked at the position, but that's not so important. You can use it to see if you need fewer "peeks" as you've trained a bit.
Blindfold chess has always been used in training. You'll get better at visualizing in your own games, and once you've played a few games blindfolded, you'll notice it gets easier and easier. It's also, of course, a good concentration exercise. And a skill you can use when traveling long distances by car or train with other chess players :-)
Something you can then do to increase the difficulty is to play openings you're not very familiar with. I tried it earlier today, and it was immediately harder to remember where the pieces were, since they weren't in their usual places. Especially the pawns became difficult to keep track of.