If you just want to retrieve those three values, you can pass an out-parameter to preg_match like this:
preg_match(
'~^([A-z])([0-9]+)-([^/]*)$~' ,
'A123-boooooo',
$matches
);
$fullMatch = $matches[0]; // 'A123-boooooo'
$letter = $matches[1]; // 'A'
$number = $matches[2]; // '123'
$word = $matches[3]; // 'boooooo'
// Therefore
$A = array_slice($matches, 1);
If you want to do the replacement right away, use preg_replace:
$newString = preg_replace(
'~^([A-z])([0-9]+)-([^/]*)$~',
'index.php?tt=$1&ii=$2&ll=$3',
'A123-boooooo
);
The documentation of these is usually really good for further information.