In GridView how to insert the data and that data to be saved in database

<asp:gridview id="GridView1" runat="server" autogeneratecolumns="false" xmlns:asp="#unknown">
            AllowSorting="True">
        <columns>
                <asp:templatefield headertext="SNO">
                    <edititemtemplate>
                        <asp:textbox id="txtSNO" runat="server" text="<%# Bind("SNO") %>"></asp:textbox>
                    </edititemtemplate>
                    <itemtemplate>
                      <asp:label id="lblSNO" runat="server" text="<%# Bind("SNO") %>"></asp:label>
                    </itemtemplate>
                </asp:templatefield>
                
                <asp:templatefield headertext="Name">
                    <edititemtemplate>
                        <asp:textbox id="txtName" runat="server" text="<%# Bind("Name") %>"></asp:textbox>
                    </edititemtemplate>
                     <itemtemplate>
                      <asp:label id="lblName" runat="server" text="<%# Bind("Name") %>"></asp:label>
                    </itemtemplate>
                </asp:templatefield>
                
                <asp:templatefield headertext="Age">
                    <edititemtemplate>
                        <asp:textbox id="txtAge" runat="server" text="<%# Bind("Age") %>"></asp:textbox>
                    </edititemtemplate>
                     <itemtemplate>
                      <asp:label id="lblAge" runat="server" text="<%# Bind("Age") %>"></asp:label>
                    </itemtemplate>
                </asp:templatefield>

                <asp:templatefield headertext="Address">
                    <edititemtemplate>
                        <asp:textbox id="txtAddress" runat="server" text="<%# Bind("Address") %>"></asp:textbox>
                    </edititemtemplate>
                     <itemtemplate>
                      <asp:label id="lblAddress" runat="server" text="<%# Bind("Address") %>"></asp:label>
                    </itemtemplate>
                </asp:templatefield>
            </columns>
            <selectedrowstyle forecolor="#CCFF99" font-bold="True">
                BackColor="#009999"></selectedrowstyle>
            <rowstyle forecolor="#003399" backcolor="White"></rowstyle>
        </asp:gridview>

<asp:button id="btnAddNewRow" runat="server" text="AddNewRow" onclick="BtnAddNewRowClick" xmlns:asp="#unknown" />
<asp:button id="btnInsert" runat="server" text="Insert" onclick="BtnInsertClick" xmlns:asp="#unknown" />

[Serializable]
internal class Sample
{
    public static  Sample CreateTestSample(int i)
    {
        return new Sample
                   {
                       SNO = "SNO " + i,
                       Address = "Address " + i,
                       Age = i,
                       Name = "Name " + i,
                       City = "City " + i
                   };
    }
    
    public string SNO { get; set; }
    public string Name { get; set; }
    public string City { get; set; }
    public int Age { get; set; }
    public string Address { get; set; }
}

private List<sample> DataSamples
{
    get { return  ViewState["Samples"] as List<sample>; }
    set { ViewState["Samples"] = value; }
}

protected void Page_Load(object sender, EventArgs e)
       {
           // Fill GridView for First Time
           if (!IsPostBack)
           {
               FillGrid();
           }
       }

private void FillGrid()
        {
            // For test sapmle code
            DataSamples = CreateDataSamples();
            GridView1.DataSource =DataSamples ;
            GridView1.DataBind();

            //TODO:There are more ways to retreiving data from db
            // e.g SqlDataAdapter
            // SqlConnection cs = new SqlConnection("Data Source=.\\SQLEXPRESS; Initial Catalog=dbName; Integrated Security=TRUE");
            // SqlDataAdapter da = new SqlDataAdapter();
            // cs.Open();
            // da.SelectCommand = new SqlCommand("SELECT * FROM table", cs);
            // da.Fill(dg);
        }
        private List<sample> CreateDataSamples()
        {
            var list = new List<sample>();
            for (int i = 0; i < 10; i++)
                list.Add(Sample.CreateTestSample(i));
            
            return list;
        }

protected void BtnAddNewRowClick(object sender, EventArgs e)
        {
            var list = CreateDataSamples();
            list.Add(new Sample());
            
            GridView1.EditIndex = list.Count - 1;
            GridView1.DataSource = DataSamples;
            GridView1.DataBind();
        }

protected void BtnInsertClick(object sender, EventArgs e)
        {
            var row = GridView1.Rows[GridView1.EditIndex];
            var sno = ((TextBox) (row.FindControl("txtSNO"))).Text;
            var name = ((TextBox) (row.FindControl("txtName"))).Text;
            var age = Convert.ToInt32(((TextBox) (row.FindControl("txtAge"))).Text);
            var address = ((TextBox) (row.FindControl("txtAddress"))).Text;

            var newSample = new Sample
                                {
                                    SNO = sno,
                                    Name = name,
                                    Age = age,
                                    Address = address
            
                                };
            //Save Data in Persistent Data
            //TODO you should write your own code for update DB
            if (GridView1.EditIndex > 0)
                DataSamples[GridView1.EditIndex] = newSample;

            GridView1.EditIndex = -1;
            GridView1.DataSource = DataSamples;
            GridView1.DataBind();

        }