If you haven't emptied the Trash, you can pull it back out of the Trash. If you have emptied it, it's doubtful you can retrieve it. Search the forum for "file recovery" or "data recovery" and you'll find many threads with recommendations of apps that might help, such as:Okay so I accidentally deleted a word document that i really really need, is there a way to restore it?
Word of advice. Setup a DropBox account for critical documents and consider a Time Machine backup for your Mac.
i have no idea how to use time machine