How to Insert (Save) Data in SQL using Two Tier Architecture ASP.Net

First you create a class, wirte an Insert method passing an object as a parameter.

public class Insert
{
    public string FirstName { get; set; }
    public string Salary { get; set; }
    public string Gender { get; set; }
    //Connection string to connect to database
    string ConnectionString = "Server=sa;Database=xyz;User Id=sa; password=sa123";
    public void insertmethod(Insert add)
    {
        using (SqlConnection con = new SqlConnection(ConnectionString))
        {
            //Create the SqlCommand object
            SqlCommand cmd = new SqlCommand("spAddEmployee", con);
            //Specify that the SqlCommand is a stored procedure
            cmd.CommandType = System.Data.CommandType.StoredProcedure;

            //Add the input parameters to the command object
            cmd.Parameters.AddWithValue("@Name", add.FirsName);
            cmd.Parameters.AddWithValue("@Gender", add.Gender);
            cmd.Parameters.AddWithValue("@Salary", add.Salaray);

            //Open the connection and execute the query
            con.Open();
            cmd.ExecuteNonQuery();


        }
    }
}

<table style="border: 1px solid black; font-family:Arial">
    <tr>
        <td>
            Employee Name
        </td>
        <td>
            <asp:TextBox ID="txtEmployeeName" runat="server"></asp:TextBox>
        </td>
    </tr>        
    <tr>
        <td>
            Gender
        </td>
        <td>
            <asp:DropDownList ID="ddlGender" runat="server">
                <asp:ListItem>Male</asp:ListItem>
                <asp:ListItem>Female</asp:ListItem>
            </asp:DropDownList>
        </td>
    </tr> 
    <tr>
        <td>
            Salary
        </td>
        <td>
            <asp:TextBox ID="txtSalary" runat="server"></asp:TextBox>
        </td>
    </tr>       
    <tr>
        <td colspan="2">
            <asp:Button ID="btnSubmit" runat="server" Text="Submit" 
                onclick="btnSubmit_Click" />
        </td>
    </tr>          
    
</table>

//code behind of Aspx.cs

//Now create an object of Insert class
Insert add=new Insert();
protected void btnSubmit_Click(object sender, EventArgs e)
{
add.FirstName=txtEmployeeName.Text;
add.Gender=ddlGender.SelectedItem.Text;
add.Salary=txtSalary.Text;
//calling add method and passing object 
add.insertmethod(add);
}