If you want to read it all into memory, a simple File.ReadAllText() will do just fine. If your file is indeed very large, then you can use the StreamReader class, see the below approach. It is sometimes inevitable but should mostly be avoided for style reasons.
im file As New FileInfo("path\to\file")
Using reader As StreamReader = file.OpenText()
While Not reader.EndOfStream
Dim nextLine As String = reader.ReadLine()
The challenges on large read, is discussed in detail at http://kirillosenkov.blogspot.com/2007/11/please-use-filereadalltext-and-like.html