Use the IO.StreamWriter object to write to the file:
Dim writer As New IO.StreamWriter("path to the file", True)
First argument is the path to the file, and the second argument which is a boolean indicates whether you want to append to the file.
To open a file and read it use the IO.StreamReader object:
Dim reader As New IO.StreamReader("path to the file")
'then read it using different methods...
reader.ReadLine()
'or
reader.ReadToEnd()
'or other reading methods you want to use that you want to use