Check out example codes for "unity3d raycast". It will help you in understanding the concepts better.

Code Example 1

using UnityEngine;

// C# example.

public class ExampleClass : MonoBehaviour
{
    void Update()
    {
        // Bit shift the index of the layer (8) to get a bit mask
        int layerMask = 1 << 8;

        // This would cast rays only against colliders in layer 8.
        // But instead we want to collide against everything except layer 8. The ~ operator does this, it inverts a bitmask.
        layerMask = ~layerMask;

        RaycastHit hit;
        // Does the ray intersect any objects excluding the player layer
        if (Physics.Raycast(transform.position, transform.TransformDirection(Vector3.forward), out hit, Mathf.Infinity, layerMask))
        {
            Debug.DrawRay(transform.position, transform.TransformDirection(Vector3.forward) * hit.distance, Color.yellow);
            Debug.Log("Did Hit");
        }
        else
        {
            Debug.DrawRay(transform.position, transform.TransformDirection(Vector3.forward) * 1000, Color.white);
            Debug.Log("Did not Hit");
        }
    }
}

Code Example 2

using UnityEngine;

// C# example.

public class ExampleClass : MonoBehaviour
{
    void Update()
    {
        // Bit shift the index of the layer (8) to get a bit mask
        int layerMask = 1 << 8;

        // This would cast rays only against colliders in layer 8.
        // But instead we want to collide against everything except layer 8. The ~ operator does this, it inverts a bitmask.
        layerMask = ~layerMask;

        RaycastHit hit;
        // Does the ray intersect any objects excluding the player layer
        if (Physics.Raycast(transform.position, transform.TransformDirection(Vector3.forward), out hit, Mathf.Infinity, layerMask))
        {
            Debug.DrawRay(transform.position, transform.TransformDirection(Vector3.forward) * hit.distance, Color.yellow);
            Debug.Log("Did Hit");
        }
        else
        {
            Debug.DrawRay(transform.position, transform.TransformDirection(Vector3.forward) * 1000, Color.white);
            Debug.Log("Did not Hit");
        }
    }
}
This example creates a simple Raycast, projecting forwards from the position of the object's current position, extending for 10 units.

using UnityEngine;

public class ExampleClass : MonoBehaviour
{
    void FixedUpdate()
    {
        Vector3 fwd = transform.TransformDirection(Vector3.forward);

        if (Physics.Raycast(transform.position, fwd, 10))
            print("There is something in front of the object!");
    }
}

Learn ReactJs, React Native from akashmittal.com