The game was going great for you.
What a nice moyo. Opponent who came into the center of it really deserved to die. Moyos aren’t especially popular these days because it’s considered too easy to destroy or reduce them. But in practice people die all the time in them, even low dans, I recently forced even 3d and 4d to die. Sometimes even EGF dans die. But good shapes in killing can be hard to explain, a lot of them are intuitive.
1 is often good shape for attacking, one space from the lone stone. Closer and it might strengthen black, further and it’s not as severe.
Always peep at everything. You want your opponent to have heavy eyeless shapes. But always remember that opponent might ignore your peep. Or extend instead of connecting straight away. White three stones aren’t in danger, the only thing to worry about is getting squeezed but white is strong there so free moves black places there face pretty strong white so it should be ok. If you think about it, it would be pretty sad if white had to defend there. They’re so strong and still have to defend?
Black making this shape is a bad sign for white. It’s becoming close to alive now. Note that there’re no white stones around it so it has place to expand. That’s an important quality here, not just empty intersection inside of it. If it was more surrounded by white stones, the shape would be much sadder.
This feels so overcommitting. Ideally you want to kill opponent in easy and fun way. Where at any point, if things go south, you can back off and be ok with the result. Which is why AI might suggest playing A. After all, black is not alive yet and white does solidify area towards the bottom. But the move you played commits to killing, it gives black a bunch of free moves like Black A. And like if black lives then you would’ve liked to have spend this move elsewhere. So it’s like you’re saying “I definitely kill you, black, this move is crude but it doesn’t matter since you’re dead now, you just don’t know it yet”. This type of committing move shows that situation is slipping from white’s control. Though white is still pretty strong all around, I wouldn’t be sure I could live with black, maybe it’s still ok.
And so on and so forth.
Fighting is hard because it’s so involved. There’re a lot of considerations, shapes and reading. I suspect some teachers avoid going into it. I often see lessons skip through fights with only basic commentary (well, maybe live commentary go into it because they have lots of time). But it’s an interesting topic. It’s fascinating to see a pro show the actual reasoning for their moves with dozen-move follow-ups.
Good practice for this type of fighting is shape game. Black has stones on all first line intersections and has to kill all white to win, white has to live with something to win.
Also Antti made a lecture on something like that.