Here is the most basic and easy way to represent data in the grid view form.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Data.SqlTypes;
 
namespace FormsApplication1
{
    publicpartialclassForm4 : Form
    {
 
        public Form4()
        {
            InitializeComponent();
        }
 
        publicvoid fill()
        {
            SqlConnection con3 = newSqlConnection();
            con3.ConnectionString = (@"Data Source=msclient-012\sqlexpress;Initial Catalog=testing_st;User ID=sa;Password=mindstick");
            DataSet ds = newDataSet();
 
            con3.Open();
            SqlCommand cmd = newSqlCommand("select A.Enrollment_number,A.Student_name,A.Father_Name,A.Mother_Name,A.Sex,A.Permanent_Add,A.Permanent_State,B.Subject_Maths,B.Subject_Physics,B.Subject_Chemistry,B.Subject_English,B.Subject_Hindi,B.Subject_Social,B.class FROM Std_Details A,Std_Opt_Sub B where A.Enrollment_number = B.Enrollment_number", con3);
            SqlDataAdapter da = newSqlDataAdapter();
            da.SelectCommand = cmd;
            da.Fill(ds);
            dataGridView1.DataSource = ds.Tables[0];
 
        }
    }
}