One meaning of oppure is otherwise. Otherwise can be adverb or conjunction.
adverb
a)
Otherwise I don' t believe him.
conjunction
b)
I lent him the money, otherwise he wouldn't have been able to pay the rent.
In case a) otherwise is a pronominal adverb, it stands for something, for an idea (If he can' t prouve it / If he doesn't give me my money back....I don't believe him). In case b) it is just a conjunction. Otherwise can be translated with oppure or altrimenti, but only oppure can be used as an adverb and a conjunction. As an adverb oppure can be substituted with altrimenti. This substitution is not possible in the use as a conjunction.
oppure = or, otherwise altrimenti = otherwise
To keep it simple. Altrimenti is only a conjunction.
Vorresti smettere di lavorare e studiare a tempo pieno oppure vuoi farlo di notte, magari riducendo l'orario di lavoro?
Would you like to stop working and dedicate your whole time to your studies or would you like to study at night, perhaps with reduced working hours?
Devi essere proprio innamorato per desiderare di stare con lei nonostante tutto, oppure pensi di ritornarci semplicemente per vendicarti?
You must be really in love if you wish to stay with her after all what happened or do you wish to return only to avenge yourself.
Quando state in una nuova compagnia, piena di persone che ancora non conoscete, preferite stare zitti e ascoltare oppure parlare?
If you stay with people you don' t know already do you prefer to keep silence and listen or to speak?
Oppure used as an pronominal adverb. Substitution with altrimenti possible.
Se qualcuno ha qualche idea sono felice di ascoltare altrimenti mi dedicherò ad altri progetti. Grazie a tutti per l'aiuto.
Se qualcuno ha qualche idea sono felice di ascoltare oppure mi dedicherò ad altri progetti.
If someone has an idea I would be glad to listen to him, otherwise I dedicate myself to other projects.
The same meaning as oppure has the simple o, but together with other conjunctions only o can be used.
Non ha neppure bevuto il caffè, forse non ne aveva voglia, o forse le mancavano le forze per arrivare alla tazzina.
He not even drunk coffee, perhaps he didn't want or perhaps he was just to feeble to reach the cup.
Ora mi chiedo: non ne aveva voglia oppure semplicemente non ha capito quello che volevo?
No I ask myself: Didn' t he want to do it or didn' t he understand what I wanted?
The construction either... or is formed with o ... o.
O non ne aveva voglia, o non credeva fosse il caso, oppure non credeva occorresse drammatizzare.
Either he didn' t want or he believed that' s not the case, or perhaps he believed that there is no need to dramatize.
