Edit the custom outline

You can create your own custom shape and edit it in two ways. The first way is by automatically generating an outline, and then moving the control points of the generated outline to further refine its shape. Alternatively click and drag over any space in the Custom Outline editor window to create a rectangular outline with four control points and begin refining the outline by moving the control points or adding and removing them.

Click and drag over the SpriteA 2D graphic objects. If you are used to working in 3D, Sprites are essentially just standard textures but there are special techniques for combining and managing sprite textures for efficiency and convenience during development. More info
See in Glossary texture in the editor window to create rectangle outlines with four control points. Repeat this step to create multiple MeshThe main graphics primitive of Unity. Meshes make up a large part of your 3D worlds. Unity supports triangulated or Quadrangulated polygon meshes. Nurbs, Nurms, Subdiv surfaces must be converted to polygons. More info
See in Glossary outlines within the Sprite. Unity only renders the areas enclosed within the Mesh outlines.