password cracker?

how do aqw password crackers work? i get the hole concept of adding usernames but i dont get how it tells you wich password belongs to wich account

for example how does it figure out that

[password] that this is a paswword for [insert username]

Well i can help you if your a coder if you arnt then you wont understand how it works :/

Add me on skype:cody.devil