Generally speaking to fail is a verb, while a failure is either an action that failed or a person that is horribly unsuccessful.Fail is also used as a slang term to mean failure in the sense of an attempted action, for instance a person falling off their skateboard. Hope this helps.

Failure is the broad sense of the term fail You can say, he is a failure, the mission was a failure. with fail, it's mostly used as a verb, he failed the test. Stubbed means to accidentally hit something. it's mostly used to say that you hit your toe. I stubbed my toe against the table.