Inserting text using Word object model

How would I insert text into a Rich Text Box using the Word object model?

Here is a code snippet:

using System;
using System.Windows.Forms;
using Microsoft.Office.Interop.Word;
using Microsoft.Office.Interop;



namespace Plant_A_Tree
{
    public partial class Plant_Tree_Main_Interface : Form
    {
        Selection selection;

        public Plant_Tree_Main_Interface()
        {
            InitializeComponent();
        }

   
        private void Plant_Tree_Main_Interface_Load(object sender, EventArgs e)
        {
           
                



        }

        private void btnInsert_Text_Click(object sender, EventArgs e)
        {


selection = new Selection();  // This may generate an error.

            selection.InsertBefore("Hello, John!"); //This Generates an error and needs to be fixed.





        }
    }
}