I’d also be happy if there was a properly indexed ordered manual you could read front to back, starting with basic concepts and gradually moving into advanced techniques or special features. Unity and 3DSMax have it, just to name two, and it has been very useful for me.
However, I don’t think you need to worry about wrong answers in the forum. I very rarely see that and when it happens other people are very fast to correct it. I’d argue you can get better answers in the forum where professional trainers, extension developers and people with other perspectives can fill in each others answers.
One person might say the difference between groups and components is that components can share a common definition if they are identical, which allows you to edit them all at once as well as keeping down the file size. If I’m not mistaken this is how the help center puts it. However, in the forum someone would be quick to add that groups also share definition after being copied, until they are opened for editing at which point they are implicitly made unique. The former might be a more pedagogical way of putting it that most people are happy with, but the latter is the actual behavior of the program, and allows you to do a few useful things like converting identical groups into components with a shared definition at a later point. The point is that the forum gives you both perspectives.
For systematic information about the program itself, I’d ignore the help center where topics can span vaguely defined tasks, and use the status text and instructor inside of SketchUp. These sources should cover everything a tool does in a very consistent and concise way.