KeyCode.Mouse0

Description

The Left (or primary) mouse button.

Use this to detect left mouse button presses. The “0” mouse button is the main button on the user’s mouse, which is usually the left mouse button.

using UnityEngine;

public class Example : MonoBehaviour
{
    void Update()
    {
        //Detect if the left mouse button is pressed
        if (Input.GetKey(KeyCode.Mouse0))
        {
            Debug.Log("Mouse 0 ");
        }
    }
}