Im using microsoft visual studio and im making a calculator for a project but Im missing somethings. Can someone review and help me in detail?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace calculator2
{


public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}

protected void Button1_Click(object sender, EventArgs e)
{
TextBox1.Text = TextBox1.Text + D1.Text;
}

protected void D2_Click(object sender, EventArgs e)
{
TextBox1.Text = TextBox1.Text + D2.Text;
}

protected void D3_Click(object sender, EventArgs e)
{
TextBox1.Text = TextBox1.Text + D3.Text;
}

protected void D4_Click(object sender, EventArgs e)
{
TextBox1.Text = TextBox1.Text + D4.Text;
}

protected void D5_Click(object sender, EventArgs e)
{
TextBox1.Text = TextBox1.Text + D5.Text;
}

protected void D6_Click(object sender, EventArgs e)
{
TextBox1.Text = TextBox1.Text + D6.Text;
}

protected void Button7_Click(object sender, EventArgs e)
{
TextBox1.Text = TextBox1.Text + D7.Text;
}

protected void D8_Click(object sender, EventArgs e)
{
TextBox1.Text = TextBox1.Text + D8.Text;
}

protected void Button9_Click(object sender, EventArgs e)
{
TextBox1.Text = TextBox1.Text + D9.Text;
}

protected void Bminus_Click(object sender, EventArgs e)
{
string fnum = TextBox1.Text;
TextBox1.Text = "";
string operation = "subtraction";
}

protected void D0_Click(object sender, EventArgs e)
{
TextBox1.Text = TextBox1.Text + D0.Text;
}

protected void Button12_Click(object sender, EventArgs e)
{
string fnum = TextBox1.Text;
TextBox1.Text = "";
string operation = "addition";
}

protected void Bmult_Click(object sender, EventArgs e)
{
string fnum = TextBox1.Text;
TextBox1.Text = "";
string operation = "multiply";
}

protected void Bclear_Click(object sender, EventArgs e)
{
TextBox1.Text = "";
}


protected void Benter_Click(object sender, EventArgs e)
{

string anum = TextBox1.Text;
int Benter = Convert.ToInt16(anum);
int snum = Convert.ToInt16(fnum);


}




}
}