"She enters the restaurant."
Translation:Lei entra nel ristorante.
"entrare" needs a preposition.
Entrare in un posto = Enter in a place
Entrare da qualche parte = Enter somewhere
Entrare a casa = Enter home
The most common preposition is IN, but as you can see there are some exceptions.
Here a useful list but, there is not the verb "entrare" and for movement verbs you can have "in" that replaces "a" in the most of the cases. If there will be some questions regarding the issue, I will find a way to explain it in a second moment. http://italian.about.com/od/verbs/a/aa031908a.htm
O.K so because this is a movement verb when you are entering somewhere, you are not just entering "the" restaurant, or il ristorante, but for Italian grammar, you are entering "in" the restaurant, or nel ristorante, yes? Oh boy, as someone already said, yet another layer. Thank you for this explanation. Where would all of us be without our community?