One game of Spades followed from the deal to the finish, move by move, with the reason for each choice.
You and Bo are partners, sitting opposite each other; Ada and Cleo are the other partnership. Cleo deals, so the bidding and the first lead start with you, on her left. Your hand: ♠ A K 9 6 3, ♥ A 7 2, ♦ Q 8 4, ♣ K 5.
Count your tricks. A♠ and K♠ should win, A♥ should win once, and five spades usually take one more trick at the end when the others run out. The K♣ may or may not win. You bid 4.
Ada bids 4. Bo bids 3, so your partnership has promised 7 tricks between you. Cleo bids nil: a promise to take no tricks at all, scored on its own, worth 100 if she keeps it and minus 100 if she does not. Her partnership's contract is Ada's 4.
A nil changes the whole hand. Ada will now try to protect Cleo by winning the tricks Cleo might otherwise be stuck with, and you and Bo can earn 100 points just by forcing Cleo to take one.
Spades cannot be led until one has been played, so you lead A♥. Ada plays 5♥, Bo 3♥, and Cleo throws K♥ under your ace — exactly what a nil bidder wants to do with high cards. You win the trick.
You lead 2♥. Ada plays 10♥. Bo has no hearts left, so he trumps with 5♠ and wins the trick for your side. Cleo plays 9♥. That spade breaks spades, and from now on anyone may lead them.
Over the next nine tricks your A♠ and K♠ win, you ruff a club once your K♣ and 5♣ are gone, and Bo takes two more. Ada wins four, using her high cards to take tricks that Cleo would otherwise have been forced to win.
By trick twelve your side has 7 tricks, Ada has 4, and Cleo has none. Cleo has two cards left: J♦ and 2♠.
You lead 4♦, a low diamond. Ada has no diamonds and no spades left, so she can only throw a club. Bo plays 2♦. Cleo must follow suit, and her only diamond is the jack, which wins the trick. Her nil is broken.
On the last trick Cleo leads 2♠, and your 9♠ wins it. The final count: your partnership 8 tricks, Ada 4, Cleo 1.
Your side bid 7 and took 8: 70 points for the contract and 1 for the overtrick, which is also your first bag. Ada and Cleo bid 4 and took 5 between them, since Cleo's trick counts for the partnership: 40 plus 1 for a bag. But Cleo's nil failed, which costs 100, so they score minus 59.
After one hand it is 71 to minus 59. The first partnership to 500 wins, and every tenth bag costs a hundred along the way.