Translation:The man eats dinner.
Cena is being used as a verb in this case - and it means "to dine/to eat dinner/to have dinner". It's a bit confusing because the third person singular form of the verb "cenare" (the form you use with lui/lei/it/the man/etc) is identical to the noun "il cena" which means "the dinner".
No, not really. When we say in English "The man is having dinner," we mean that he is eating his evening meal (unless you live in one of those places where "dinner" refers to the midday meal, but that's another issue). In Italian, that is simply "L'uomo cena." The verb "cenare" means "to have dinner" or "to eat dinner" or (in more stilted language) "to dine." In sriram385's sentence "L'uomo ha la cena" the word "ha" means "has" in the sense of possessing dinner, not consuming it. So you might theoretically hear one waiter asking another waiter if a customer has received his dinner yet, and the second waiter would answer "Si, l'uomo ha la cena," but that just means that the dinner is on the table in front of the man, not that he is eating it.
io pranzo for lunch, io ceno for dinner.
Pranzare is the infinitive:
I eat lunch = io pranzo
you eat lunch = tu pranzi
he/she eats lunch = lui/lei pranza
we eat lunch = noi pranziamo
you eat lunch = voi pranzate
they eat lunch = loro pranzano
I eat dinner = io ceno
you eat dinner = tu ceni
he/she eats dinner = lui/lei cena
we eat dinner = noi ceniamo
you eat dinner = voi cenate
they eat dinner = loro cenano
I have been called wrong in the past when saying, "lui pranza" meant "he eats lunch." I thought maybe it was because "mangia" wasn't bring used and it meant, "he has lunch." Usually, when "cena" is used as a verb, I use "dine" and it's perfectly acceptable. On this particular question, I get dinged. Am I wrong or the program? I tend to think I'm wrong.