What to teach: At school, it's critical in what order and at what age children learn things. If they are out of step with what's expected, they can be left behind. That isn't an issue with individual learning, and therefore you don't have to worry so much. Parents can follow a curriculum if they want, or they can introduce ideas whenever opportunities arise or whenever children take an interest. If the child (or parent) later realises they didn't learn something important which they now need, they simply learn it at that point.
For example, my eldest learned basic maths through daily life. By their teens, they were functionally numerate, but not ready for advanced study. When they wanted to sit maths GCSE, they simply got hold of a textbook, discovered which aspects they hadn't yet covered, and learned the material there and then. That took just nine months. Schools require years and years to cover the maths curriculum because mass instruction is so inefficient compared with targeted learning, and because in many cases the curriculum requires them to push abstraction too young, before the child has acquired enough experience to grasp it easily, so it's a hard slog with much wasted effort.
By the same token, it's apparent to me that my younger child needs more relationship education, as she is vulnerable and easily manipulated. So that has become a focus for her. I look out for materials which will engage her, ask other parents for recommendations, and have discussions with her. I would have preferred her to learn this when she was younger, but she wasn't ready. Fortunately, there is no deadline. She can learn it now.
How to teach: Most home educating parents don't use the school model of formal instruction. Instead, we help our children find resources which are right for them. For instance, when one of my kids wanted to learn German, we both looked around for methods which suited them. They've done Duolingo off and on, watched TV documentaries in German, listened to Harry Potter audiobooks in German, attended lessons, and did a stint as an au pair. They love singing, and have German pop songs on a playlist.
I know that sounds rather haphazard. It IS rather haphazard. Learning often is. That doesn't mean it's less effective than systematic instruction. I'm quite shocked at how little German my younger teen's best friend actually understands after being taught it for 2.5 years at school! Whatever they're doing in her classes, it clearly isn't right for her.
Engaging dozens of kids in learning the same thing at the same time, whether or not they are ready or interested, is a tall order. Ascertaining what each of them has actually taken on board is also difficult when you don't know them well, you don't have time for one-to-one conversations, and you can't observe them going about their lives in a range of situations. Classroom teachers do require many skills which I lack. But the environment in which my few children are learning is not like a school, and so my job is easier than you're imagining.