How to instantiate the prefabs on grid in Unity?

I've tried to create the gameObject such as 'cube' on Input.mousePosition. I mean, whatever gameObject or prefabs are instantiated when i click any position on screen and it worked very well. However, what i really want to do is that the gameObject or prefabs are instantiated on specified area so i'm struggling with panel and grid to figure out. No matter how to do, I just want to create cloned gameObject on Input.mousePosition in specified area. Is there a way to restrict the size of screen or to resize the grid (ex. 1/4 of panel and bottom left). Please let me knot how to figure it out. Thank you.

This is the code what i've done below.

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class point : MonoBehaviour
 {
 public GameObject particle;
 Ray ray;
 RaycastHit hit;
 public Vector2 pos1;
 
 void Start () {
 }
 
 void Update (){
 
     Vector3 mousePos=new Vector3(Input.mousePosition.x, Input.mousePosition.y, 0f);
 
     if (Input.GetMouseButtonDown (0)) {
         pos1 = new Vector2 (Input.mousePosition.x, Input.mousePosition.y);
         //Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
         Debug.Log (Input.mousePosition.x);
         Debug.Log (Input.mousePosition.y);
 
         Vector3 wordPos;
         Ray ray=Camera.main.ScreenPointToRay(mousePos);
 
         if(Physics.Raycast(ray,out hit,1000f)) {
             wordPos=hit.point;
         } else {
             wordPos=Camera.main.ScreenToWorldPoint(mousePos);
         }
         Instantiate(particle,wordPos,Quaternion.identity); 
 
     }
 
 }
 }