How to...

    fileReader = My.Computer.FileSystem.ReadAllText("Text.txt")
        If ListBox1.SelectedItem = "Test" Then
            RichTextBox1.Text = fileReader
        End If

dim reader as New StreamReader("Text.txt") 
 If ListBox1.SelectedItem = "Test" Then
            RichTextBox1.Text = reader.ReadLine
        End If

dim reader as New StreamReader(listbox1.SelectedItem + ".txt") ' will grab the user clicked event on listbox1 and open that txt file
 RichTextBox1.Text = reader.ReadLine ' reads txt file by 1 line. you would have to either do a For Each loop or a While loop to get each line or do ReadToEnd

Imports System****
Public Class Form2
    Private Sub ListBox1_SelectedIndexChanged(sender As System.Object, e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
        'ListBox1.Items(ListBox1.SelectedIndex)
    End Sub

    Private Sub Form2_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        RichTextBox1.Clear()
        ListBox1.Items.AddRange(IO.File.ReadAllLines("ListB.txt"))
    End Sub

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        IO.File.WriteAllLines("ListB.txt", (From p As String In ListBox1.Items Select p).ToArray)
        IO.File.WriteAllLines(TextBox1.Text & "/" & "code.txt", From n As String In RichTextBox1.Text Select n)
    End Sub

    Private Sub TextBox1_TextChanged(sender As System.Object, e As System.EventArgs) Handles TextBox1.TextChanged

    End Sub

    Private Sub RichTextBox1_TextChanged(sender As System.Object, e As System.EventArgs) Handles RichTextBox1.TextChanged

    End Sub

    Private Sub TextBox2_TextChanged(sender As System.Object, e As System.EventArgs) Handles TextBox2.TextChanged

    End Sub

    Private Sub ListBox1_DoubleClick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBox1.DoubleClick

        Dim Test As New Long
        'Dim test As New String = IO.File.ReadAllLines(" // needs doing
        IO.File.ReadAllLines("ListB.txt")
        'IO.File.ReadLines
        'If ListBox1.SelectedIndex = 
        Select Case ListBox1.SelectedIndex
            Case 0
                RichTextBox1.Text = "Code here"
            Case 1
                RichTextBox1.Text = "Code1 here"
            Case 2
                RichTextBox1.Text = "Code2 here"
        End Select
    End Sub
End Class

<?xml version="1.0" encoding="utf-8"?>
<main> 
</main>

Imports System****

Public Class Form1



    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim xdoc As New Xml.XmlDocument
        xdoc.Load("list.xml")
        Dim titleNode As Xml.XmlNode = xdoc.Item("main")
        Dim NewElement As Xml.XmlElement
        NewElement = xdoc.CreateElement("title") ' creates new element <title>valuehere</title>
        NewElement.InnerText = TextBox1.Text
        titleNode.AppendChild(NewElement)
        xdoc.Save("list.xml") ' Saves the xml file with the content added
        ListBox1.Items.Clear()
        UpdateList()
        Dim path As String = TextBox1.Text + ".txt"
        Dim writer As New StreamWriter(path)
        Dim text As String = RichTextBox1.Text
        writer.Write(text)
        writer.Close()
    End Sub
    Public Sub UpdateList()
        ListBox1.Items.Clear()
        Dim xdoc As New Xml.XmlDocument
        xdoc.Load("list.xml")
        Dim titleNode As Xml.XmlNode = xdoc.Item("main")
        Dim element As Xml.XmlElement


        For Each element In titleNode
            ListBox1.Items.Add(element.InnerText)
        Next
    End Sub
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ListBox1.Items.Clear()
        UpdateList()

    End Sub

    Private Sub ListBox1_MouseDoubleClick(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles ListBox1.MouseDoubleClick
        Dim loadpath As String = ListBox1.SelectedItem + ".txt"
        Dim reader As New StreamReader(loadpath)
        Do While reader.Peek() >= 0
            RichTextBox1.Text = reader.ReadToEnd()
        Loop
        reader.Close()
    End Sub

End Class