Learn Hardcore Russian: Не стоит работать поздно ночью, если утром экзамен. - It’s not worth working late at night if there is an exam in the morning.

Не стоит + infinitive is a very common impersonal way to give advice/warn someone: It’s not worth (doing X) / You shouldn’t (do X).
Grammatically, стоит is 3rd person singular of стоить (to cost / to be worth), but in this pattern it works like a modal expression, so the action comes as an infinitive: не стоит работать.

Is Не стоит работать… addressing “you,” “we,” or people in general?

It’s impersonal: literally It’s not worth working…. In real use, it’s usually advice to the listener (so effectively “you”), but it can also be general advice depending on context. If you want to make the addressee explicit, you could say Тебе не стоит работать… (You shouldn’t…).

How is не стоит different from не нужно or нельзя?

They’re different strengths/meanings:

не стоит работать = it’s not worth working (soft advice, “better not”)
не нужно работать = you don’t need to work (necessity is absent; not necessarily “bad idea”)
нельзя работать = you must not / it’s forbidden / it’s impossible to (strong prohibition or impossibility)