beginning..how to use the code, where to put it and where is it?

[softcris]

Site is ready. VirtueMart on - now the notification.php is as in Soeren's description of it: Help files.
Can't figure out where and how to make the right code for my site to accepted PayPal standard payments (inclusive credits cards)
Which file I'm looking for?
Which code do I insert in it?
After that just clic into my Merchant account in PayPal and it will go all the way perfect?
Thanks
Cris