Check out example codes for "unity create primitive". It will help you in understanding the concepts better.

Code Example 1

using UnityEngine;public class Example : MonoBehaviour
{
    // Create a plane, sphere and cube in the Scene.    void Start()
    {
        GameObject plane  = GameObject.CreatePrimitive(PrimitiveType.Plane);        
        GameObject cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
        cube.transform.position = new Vector3(0, 0.5f, 0);        
        GameObject sphere = GameObject.CreatePrimitive(PrimitiveType.Sphere);
        sphere.transform.position = new Vector3(0, 1.5f, 0);       
        GameObject capsule = GameObject.CreatePrimitive(PrimitiveType.Capsule);
        capsule.transform.position = new Vector3(2, 1, 0);       
        GameObject cylinder = GameObject.CreatePrimitive(PrimitiveType.Cylinder);
        cylinder.transform.position = new Vector3(-2, 1, 0);
    }
}

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