FUNDAMENTALS OF COMPUTER

Detailed explanation-1: -A Sorting Group is a component which alters the order in which Sprite Renderers do their rendering. It allows a group of Renderers which share a common root to be sorted together. Renderers in Unity are sorted by several criteria, including their order in the layer and their distance from the Camera.

Detailed explanation-2: -If you select Combine Tool with no selected vertices, you will enter Combine Vertex mode. In this mode you can selected vertices and set up some options and combine them. However, if you click on Combine button with some vertices selected, the combine action will happen immediately.