Group Box
The purpose of a group box is to group multiple Form Fields. Every Form needs at least one group box which is the root group box (also known as main box).
In that root group box you can put as many form fields as you like. You can also put another group box (or another composite field like a tab box) to create another group of fields.
The fields in the group box are arranged based on the field order and their grid data hints. This is done by the Logical Grid Layout.