Amidah

The Amidah (, "standing") is one of the two main prayers of Judaism. It has that name because people say it standing up. Jews say it at every prayer service of the year.
It is also called "Shemoneh Esrei" (, "eighteen") because at first the weekday version of the prayer had eighteen blessings. (It now has nineteen.) In the Talmud, it is called "Tefilah" (). This simply means "prayer". It has that name because it is so central to Judaism.
Blessings of the Amidah.
The Amidah always has three sections. 
Saying the Amidah.
The Amidah is said at least three times every day: at the morning, afternoon and evening prayer services. A person should say it standing. A person should say it loud enough to hear it. But it should be quiet enough that other people cannot hear it.
At the morning and afternoon services, the Amidah is repeated out loud by the prayer leader. When the Amidah is said out loud:
The Amidah is not said out loud at night.
In Reform Judaism the Amidah is not said quietly. It is said out loud at every prayer service.
Changes on Shabbat and Jewish holidays.
On Shabbat and important Jewish holidays, the Amidah prayer changes in two important ways.
There are two Amidah prayers during the year that are different from any others. See the pages on these holidays for more information.
Reference.
A "siddur" (Jewish prayer book) is always the best reference for information about Jewish prayers: 
It is a very good English/Hebrew siddur to use for learning about prayers.