Please refer this example
HTML
<asp:TextBox ID="txtEmail" runat="server" />
<asp:Button Text="Save" OnClick="Save" runat="server" />
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
<Columns>
<asp:TemplateField>
<ItemTemplate>
<asp:HiddenField ID="HiddenField1" Value='<%#Eval("Email")%>' runat="server" />
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
Namespace
using System.Data;
C#
protected void Save(object sender, EventArgs e)
{
DataTable dt = new DataTable();
dt.Columns.Add("Email");
dt.Rows.Add(this.txtEmail.Text.Trim());
this.GridView1.DataSource = dt;
this.GridView1.DataBind();
}