"Εργασία" is the equivalent of "work" in english, and "δουλειά" is the equivalent of "job".
"Εργασία" is directed to produce or accomplish something; labor; work; toil.
"Δουλειά" is a piece of work,especially a specific task done as part of the routine of one's occupation or for an agreed price (not always paid work, though).
We "work" at our "jobs", and "work" can be used to refer to our "jobs", but the underlying difference is, "work" can be used in areas where its just labour, while "job" refers to (usually) paid work.
(Again, keep in mind that in greek we sometimes use "δουλειά" for things that are not paid work. Like homework - σχολικές εργασίες για το σπίτι or house chores - δουλειές του σπιτιού.)
Ι hope I helped. ^.^
Oh, plus, an edit to my previous comment: In greek, we sometimes use δουλειά for not paid work. It's not a rule. We would still use δουλειά for paid work like
"I love my job - Αγαπώ την δουλειά μου"
"I've got two jobs - έχω δύο δουλειές."
It was just a parenthesis.
Sorry if that example confused you, its just that a school assigment and homework in english is translated into σχολική εργασία and εργασία για το σπίτι in greek. Sorry if that confused you, I just wanted to emphasize in the "not paid work, like homework" part. xP It's kinda like an exception. You'd never say school job. xP