Transfering secure certificate to my new flash / php store ?!

so i built a new flash site for a client , with a PHP checkout .
really simple .
but in her previous site she has an SSL , which is great .
but i need to incorporate that into my new php form / checkout .
can anyone give me a place to start ? sorry , im a total amateur at script , so i really just need a place to start .
oh , and im hosting the site on the same server her SSL was on before …
thanks guys !
-chris