What is a Bar Mitzvah?
Bar Mitzvah is Hebrew for “son of commandment.” When a Jewish boy turns 13, he has all the rights and obligations of a Jewish adult included in the commandments of the Torah. From that date, he will wear tefillin daily and be counted towards a minyan. This milestone, called a Bar Mitzvah, is often celebrated with a ceremony in synagogue, tefillin wearing, and parties. The celebrant may be called to the Torah, lead services, deliver a speech, or otherwise demonstrate his newfound status.
Why is this a B'nai Mitzvah and not a Bar Mitzvah?
B'nai is the plural of Bar so a Bar Mitzvah with two sons is a B'nai Mitzvah.
Minyan: The quorum of ten men necessary for communal prayer
Synagogue (Shul): A Jewish place of worship
Tefillin: Small black leather cubes containing parchment scrolls inscribed with the Shema and other biblical passages, wrapped on the arm and head of adult men during weekday morning prayers