You can add meshes to a Unity project in the following ways:
Create a 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 as part of a modelA 3D model representation of an object, such as a character, a building, or a piece of furniture. More info See in Glossary in a 3D modeling program, then import it. Unity creates a mesh asset as a part of the model hierarchy when you import a model. For more information, see Importing Models.
Create a mesh directly with in-Editor tools. Unity has built-in primitive shapes such as spheres and capsules that you can place directly into a SceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info See in Glossary. You can also use a package like ProBuilder to model a custom mesh in the Editor.