Check out example codes for "rotate to face direction". It will help you in understanding the concepts better.

Code Example 1

/// <summary>
    /// Rotate a gameobject to face a direction in 2D space with offet
    /// </summary>
    /// <param name="target"></param>
    /// <param name="RotationSpeed"></param>
    /// <param name="offset"></param>
    private void RotateGameObject(Vector3 target, float RotationSpeed, float offset)
        //get the direction of the other object from current object
        Vector3 dir = target - transform.position;
        //get the angle from current direction facing to desired target
        float angle = Mathf.Atan2(dir.y, dir.x) * Mathf.Rad2Deg;
        //set the angle into a quaternion + sprite offset depending on initial sprite facing direction
        Quaternion rotation = Quaternion.Euler(new Vector3(0, 0, angle + offset));
        //Roatate current game object to face the target using a slerp function which adds some smoothing to the move
        transform.rotation = Quaternion.Slerp(transform.rotation, rotation, RotationSpeed * Time.deltaTime);

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