Hallo Gina, Senta is both the subjuntive (conggiuntivo) and imperative (imperativo) 3er person singular form of the verb "sentire", with many meanings but in this particular case equivalent to the Deutsch " Hören Sie!"... You can use it to call te attention from ANYONE not only a "cameriere". It's also used as a way to reinforce your in the midle of a spech with someone you don't know well, because is a respect form. If you're familiar with the person, you should say "senti ". Notwithstanding, I agree with Simon. "Senta" is a rude approach, and Italians are a very form- conscious- people, and they love politeness. I'd better say "mi scusi" or "la prego" or "per cortesia"

yeah u can use it even for a cameriere, it would be better to say "mi scusi, potrebbe portarmi il conto per favore?" "excuse me could u give me the bill please?" buon studio