As Josh has stated above, you want to give each one the same name (letter, button, etc.) and all of them work. Then you want to surround all of these with a form tag:
<form name="myLetters" action="yourScript.php" method="POST">
<!-- Enter your values here with the following syntax: -->
<input type="radio" name="letter" value="A" /> A
<!-- Then add a submit value & close your form -->
<input type="submit" name="submit" value="Choose Letter!" />
</form>
Then, in the PHP script "yourScript.php" as defined by the action attribute, you can use:
$_POST['letter']
To get the value chosen.