Where does the hash come from?

[qpotential]

I'm new to all this so bear with me. I have encrypted strings using http://www.dnsqueries.com/en/encrypter.php and successfully decrypted them using oclHashcat through the HashcatGUI by BlandyUK by using the built-in clipboard function and the known encryption method.

For decrypting an encrypted file:
I have the choices of selecting a hash file or posting a hash from the clipboard. My question is what hash am I supposed to put as the input? Specifically, where does it come from in relation to the encrypted file. Is it contained somewhere in the encrypted file or is it generated from the encrypted file using an external hash generator with the encrypted file as an input?

I know this must sound retarded but I just started this adventure 2 days ago and I have searched the wiki and hundreds of websites and haven't found the answer.

Thanks in advance