A job is a specific contract with an employer, whereas work is slightly more general: It is what you do. Work can be either a verb or a noun, but job is only a noun.
I got a job in a supermarket.
My job is very boring; I'm an office clerk.
Work is tiring.
Get back to work.
If you work hard you will get promoted
Working my way through college (means "working to earn money so I can study")
Both used together
I got a job working in a dentist's office
It's a job of work (slightly unusual usage - but see these song lyrics for example http://www.mydfz.com/Paxton/lyrics/ajowtd.htm )