Captures
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Go on a nine-line board — the oldest board game still played with its original rules, and the last one computers learned to play. You place stones on the intersections to surround empty space; whoever surrounds more of the board wins. The nine-line board keeps a full game to a few minutes while leaving every idea in Go intact: capture, life and death, the ko fight, and knowing when to stop. The computer opponent plays by imagining thousands of complete games from the current position and choosing the move that wins most of them.
You are Black and move first; the computer is White and receives 6.5 points of komi as compensation. Tap an intersection once to see a faint preview stone, then tap the same point again to actually place it — one tap alone never plays a move, so a mis-tap costs you nothing.
A stone or a connected group is captured and removed the moment it has no empty point next to it. You may not play a move that leaves your own stones with no empty point unless that same move captures something. If a capture would immediately recreate the position from one move ago, that point is a ko and you must play elsewhere first before taking it back.
When neither side can gain anything, both players pass and the game is scored. This game uses area scoring under Tromp-Taylor rules: your score is your stones on the board plus the empty points surrounded only by your stones. That means dead stones still count as alive, so if the computer has stones sitting inside your territory you must actually capture them before passing.
Win the game and your streak goes up by one; lose and it resets. The computer thinks harder as your streak grows.
On a nine-line board the corners are worth far more than the centre, because a corner needs only two sides of stones to enclose territory while the middle needs four. Almost every strong opening starts on the third or fourth line near a corner, and almost every beginner's game is lost by playing the middle first and finding there is nothing to surround.
Two eyes make a group unconditionally alive, and nothing else does. An eye is an empty point completely surrounded by your own stones; a group with two separate ones can never be filled in, because your opponent would have to fill the last liberty of a group that still has another liberty, which is illegal. Every life-and-death problem you will ever see is really the question of whether a group can make two eyes or be prevented from making them.
Do not answer every move. If the computer plays somewhere small and you have a bigger point elsewhere, take the bigger point. The habit of replying locally to every stone is the single most expensive habit in beginner Go, and on a small board where each move is worth a large fraction of the total, it decides games.
Count before you fight. The board has 81 points and White starts 6.5 ahead, so Black needs 44 to win. If you can see that you are already ahead, simplify — trade off complications and take small certain profit. If you are behind, do the opposite: the losing side needs the position to stay messy.
The computer here has a specific weakness worth exploiting. It judges moves by playing out thousands of random continuations, which makes it strong at counting and capturing but blind to long forcing sequences that only pay off many moves later. Ladders and long, narrow tactical lines are where it is most likely to go wrong.