i have taken one textbox,label,and button.
when you enter text in textbox and click add button every time entered text will display in label separated by comma(,)
code:
protected void Button1_Click(object sender, EventArgs e)
{
if (Session["text"] != null)
{
string s = Session["text"].ToString();
Label1.Text =s + "," + TextBox1.Text;
Session["text"] = Label1.Text;
}
else
{
Label1.Text = TextBox1.Text;
Session["text"] = Label1.Text;
}
}