In english, we say "you should do something" which is a step down in severity from "you have to do something" or "you are supposed to do something".
In french, the verb for those two states is encompassed by "devoir".
You make the distinction with tenses!
For the case where you are suggesting something, you use the conditional tense.
For the case where you are demanding something, you use the present tense.
So the girlfriend of 2 months would say to you "tu devrais te trouver une job".
(you should get a job)
Whereas the girlfriend of two years would say "tu doit te trouver une job!"
(you must get a job!)
[Note: "une job" is not proper french. Worse, I just found out that in Québec it's "une job" and in France it's "un job"!!]
