How to create a webform that will add a string to a dictionary??

Good Evening;
I am learning C# via internet and it is becoming very difficult to figure this out.
I have a form with a textbox and a button that I want to add the text from the box to a list or dictionary when I click the button. So far I can create the list and add the text at pageload but I cannot figure out how to create the list on page load and add the text on the txtbox only after I click the button. this is the failed code.


public partial class Default2 : System.Web.UI.Page
{
    public void Page_Load(object sender, EventArgs e)
    {
        crearListado();
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        addPregunta();
    }
 
    public void crearListado()
   ...