A simple practice game — not actually playing out the dealer's hand to see whether you win or lose the hand, just practicing making the right decisions correctly according to optimal non-card-counting strategy. When you're wrong, it lets you try again, and it queues up for later review that scenario and the neighboring scenarios in the strategy table.
When you correctly hit, it gives you a random card so you can practice actually doing the arithmetic in that case and so you can practice the cases where surrender/split/double are not available; after dealing the hit card, if you don't bust, it then waits for your next decision. When you correctly split, it replaces the second card so you can practice playing out one side of the split.
The "correct" basic strategy is taken from wizardofodds.com, playing with a large shoe (4-8 decks), surrender available, double after split allowed, resplit aces allowed, and no double restriction. You can select whether to play with dealer hits or stands on soft 17, which changes the optimal play in a few specific cases. On the Vegas strip, the lower-minimum-bet tables tend to be "dealer hits on soft 17". If you've seen a basic strategy table somewhere and it didn't specify which rules it was for, it was probably "dealer stands on soft 17". Also note that the effect of playing "dealer stands" with the "dealer hits" strategy is worse than the other way around, so if you're only going to memorize one and are willing to play either, you're better off memorizing "dealer stands".
Practice modes (on the right) are:
Tested in Safari and Chrome on Mac, and in Android Browser and Chrome on Android. Also tested briefly in Firefox on Mac.