What is the "Group" option for?

Hi! My name is Mary. English is not my native language so I apologise in advance for any misunderstanding. I have a question regarding the “Group” option. I made a group that contained 3 layers, I could see each layer in “Drawing view” but not in “Camera view”. I later discovered that I couldn´t see them in camera view because they were in a Group. So I put the layers out of the group and could see them perfectly in camera view. I dont know why. Could someone explain this to me? I may be misusing this option.

Thank you very much!

When you group your layers make sure they are all plugged into a composite
which in turn is plugged into the output of the group. Make sure in turn that
the output of the group is plugged into another composite node for the rest
of your node network.

You might decide to group things to get rid of visual clutter or to organize
parts of your animation.