"I left my tools at work"------here "work" is a noun "I like to work"------here "work" is a verb "I have a new job"-----job is a noun "people have to work at their jobs" hope that helps

As nouns, "job" is countable, "work" (as a synonym of "job,") is not. "Work" can be countable in other senses, however. For example, "a work of art."

work is a verb, job is your occupation