Firstly, the CodeBank forums are for sharing code samples, not for asking questions. I've asked the mods to move this thread to the appropriate forum.

As for the question, there are various specific ways it could be done and this is just one. You can treat the original String basically as a Char array and loop through it with For Each loop. You can use the Char.IsLetter method to pick out the letters and add just them to another String. At the end of the loop, that other String will contain just the letters from the first String.