Jewish law requires all Jews over the age of majority (13 for males, 12 for females) to pray three times a day. Prayer alone is considered acceptable, but prayer with a quorum of ten adults (a minyan) is considered prayer with the community, and this is the reccomended form of prayer.
There are three prayer services each day on weekdays, and four on Shabbat (the Jewish Sabbath) and major holidays. Prayer is done almost exclusively in Hebrew, but Jewish law allows for prayers to be said in any language that the prayer understands. Orthodox synagogues use almost exclusively Hebrew, and use the local language (e.g. English) only for sermons and directions; Conservative synagogues use Hebrew for 70% to 95% of the service (depending on the local custom), and the rest is in the local language (e.g. English). Reform Temples use anywhere from 10% to 40% Hebrew; most of the service is in the local language (e.g. English).
Shacharit: morning prayers; Mincha: afternoon prayers; Ma'ariv (also: Aravit): evening prayers
On Shabbat and major holidays there is the Musaf ("additional) service that directly follows Shacharit.
Guide on the protocol & etiquette for visitors to Jewish religious service:
In most synagogues [also called Temples] it is considered a symbol of respect for all male attendees to wear a head covering, usually a dress hat or kipa (yarmulka). Kipa is a Hebrew word; yarmulka is the Yiddish word for the same thing. Kipot are usually provided near the front door; just take one and put one on as you go in. Return it to the same area on your way out of synagogue. Conservative (also called Masorti) and Orthodox synagogues ask that all male attendees cover their heads, whether they are Jewish or gentile. Most Reform (also called Progressive) Temples do not require people to cover their heads (neither Jew or gentile). Nonetheless, many Reform Jews now choose to wear a kipa.
As you might expect, there are some things that a gentile visitor should do during a Jewish religious service, and there are some things not to do.
(A) When the congregants stand, you should stand as well. This is merely a sign of respect, done when something important is happening during the service, such as the opening of the ark where the Torah is kept.
(B) When people bow at certain points during some prayers, do not bow. To follow the bowing and rising would indicate that you are actually a Jew following the halakha (Jewish law) of prayer. Since you aren't Jewish, this is not necessary.
(C) Wear modest, nice clothes. It's a house of worship.
(D) Do not wear a tallit (Jewish prayer shawl). This is only worn by Jews over the age of majority (13 for men, 12 for women.)
Want more information? Check out the following helpful website! http://ezra.mts.jhu.edu/~rabbiars/synagogue/synagogue.html
A more detailed outline of Jewish prayer services is at: http://www.jewfaq.org/liturgy.htm
Reccomended reading: "To Pray As a Jew", by Rabbi Hayim Halevy Donin "Entering Jewish Prayer" by Reuven Hammer