How to declare session variable in C#?

I want to make a new session, where whatever is typed in a textbox is saved in that session. Then on another aspx page, I would like to display that session in a label.

I'm just unsure on how to start this, and where to put everything.

I know that I'm going to need:

protected void Page_Load(object sender, EventArgs e)
{
    if (Session["newSession"] != null)
    {
        //Something here
    }
}

But I'm still unsure where to put everything.