All the children of a UI object with a Horizontal Layout Group component will be automatically placed side by side. If you allow the Horizontal Layout Group to resize the children, the children will be positioned and scaled so that they are fully within the bounds of the parent object's Rect Transform. Padding properties can be adjusted, however, if you'd like them to go outside the bounds of the parent's Rect Transform.
The order in which the children appear in the Hierarchy determines the order in which they will be laid out by the Horizontal Layout Group. The children will be laid out from left to right. The topmost child in the hierarchy will be placed in the leftmost position and the bottommost child in the hierarchy ...
