Can you explain this code? I am not able to get this?

Question

protected void btnaddtocart_Click(object sender, EventArgs e)

{

if (Session["cart"] == null)

{

SqlParameter[] prm = new SqlParameter[1];

ds = new DataSet();

prm[0] = new SqlParameter("@id", pid);

ds = an.ReturnSpParamDataSet("tbl_products_info12", prm);

if (ds.Tables[0].Rows.Count > 0)

{

DataSet pds;

pds = new DataSet();

DataTable dt = new DataTable();

dt.Columns.Add(new DataColumn("pid"));

dt.Columns.Add(new DataColumn("productname"));

dt.Columns.Add(new DataColumn("quantity"));

dt.Columns.Add(new DataColumn("price"));

dt.Columns.Add(new DataColumn("discount"));

dt.Columns.Add(new DataColumn("discountprice"));

dt.Columns.Add(new DataColumn("shippingcharge"));

pds.Tables.Add(dt);

DataRow dr = pds.Tables[0].NewRow();

dr["pid"] = pid;

dr["productname"] = ds.Tables[0].Rows[0]["product_name"].ToString();

dr["quantity"] = txtquantity.Text;

dr["price"] = ds.Tables[0].Rows[0]["price"].ToString();

dr["discount"] = ds.Tables[0].Rows[0]["discount"].ToString();

dr["discountprice"] = ds.Tables[0].Rows[0]["discountprice"].ToString();

dr["shippingcharge"] = ds.Tables[0].Rows[0]["shipingcharge"].ToString();

pds.Tables[0].Rows.Add(dr);

Session.Add("cart", pds);

}

Response.Redirect("~/cart.aspx");

}

else

{

DataSet pds = (DataSet)Session["cart"];

SqlParameter[] prm = new SqlParameter[1];

ds = new DataSet();

prm[0] = new SqlParameter("@id", pid);

ds = an.ReturnSpParamDataSet("tbl_products_info12", prm);

if (ds.Tables[0].Rows.Count > 0)

{

DataTable dt = new DataTable();

dt.Columns.Add(new DataColumn("pid"));

dt.Columns.Add(new DataColumn("productname"));

dt.Columns.Add(new DataColumn("quantity"));

dt.Columns.Add(new DataColumn("price"));

dt.Columns.Add(new DataColumn("discount"));

dt.Columns.Add(new DataColumn("discountprice"));

dt.Columns.Add(new DataColumn("shippingcharge"));

pds.Tables.Add(dt);

DataRow dr = pds.Tables[0].NewRow();

dr["pid"] = pid;

dr["productname"] = ds.Tables[0].Rows[0]["product_name"].ToString();

dr["quantity"] = txtquantity.Text;

dr["price"] = ds.Tables[0].Rows[0]["price"].ToString();

dr["discount"] = ds.Tables[0].Rows[0]["discount"].ToString();

dr["discountprice"] = ds.Tables[0].Rows[0]["discountprice"].ToString();

dr["shippingcharge"] = ds.Tables[0].Rows[0]["shipingcharge"].ToString();

pds.Tables[0].Rows.Add(dr);

Session.Add("cart", pds);

}

Response.Redirect("~/cart.aspx");

}

}