ett jobb is more colloquial, but it's still used pretty widely. Other than that, there's no real difference.
Another question - could you say "jobb" as in "er jobb är till..." or is that not the correct usage? And if I butchered that sentence I'm sorry
I'm not quite sure what you wanted to say, my best guess is 'your job is to [do this or that]', in that case, it's possible to say ert/ditt jobb är att … – the to in the English sentence in that case is an infinitive marker that goes with the verb, not a preposition.
Just out of curiosity, would it sound drastically different (or mean something else entirely) if it were "ett job"?
It would probably be pronounced /εt juːb/ [εt ʝoub] – I can only guess, maybe a moderator could tell you more.
No. The job = jobbet.
Jobben = the jobs
It's a regular word, but ett-words are a bit tricky as they use -en to mean definite plural, whereas en-words take -en to mean definite singular. You'll get the hang of it with practice and time though!