Visual Studio screenshot:
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim file_dir As String = "file.txt"
Dim sr As StreamReader = New StreamReader(file_dir)
Do Until sr.EndOfStream
TextBox1.Text += vbNewLine + sr.ReadLine()
Catch ex As Exception
In this case you are reading and adding each line to a textbox but you can read this to a string array and keep the information to work with later. It's also important to use try catch because if the file doesn't exist or you don't have permissions to read it will not crash the application.