Actually, tourists are not allowed to enter the main Vatican building; they are only allowed in the museums, including St. Peter’s Basilica, the Sistine Chapel, the Vatican Museums and Art Collections, the Square, and the Vatican Gardens. This is a common misconception, but the Vatican building itself is not accessible to tourists.
You can enter through one of the two main entrances – one that leads into St. Peter’s Basilica from the street Via Della Conciliazione. And the museum entrance that lies on the northern side off the entry road called Viale Vaticano.