A MOSQUE is a place of religious worship for Muslims
The mosque's basic parts are:
A space for people to gather and pray.

An area that points the people toward the direction of Mecca or Makkah. This is called a mihrab.

The mihrab can be a simple cutout in a wall of the mosque or it can be a very decorated area or room that has carved marble, tiles, and very patterned wood-working.
Other parts of the mosque can be:
A pulpit or minbar (an area where the leader of the prayers stands).

Minarets, towers that are used to call the Muslims to their prayers. Most mosques have one or more minarets. These towers are usually located at the four corners of the mosque.

A courtyard surrounded by columns and small rooms with wells or fountains where people may wash.

Space for a school.
Mosques can be very simple or very decorated and beautiful buildings. The three most important mosques in the world are:
The Prophet's Mosque in Medina

The Dome of the Rock in Jerusalem

The Great Mosque in Makkah
THE PROPHET'S MOSQUE IN MEDINA
THE DOME OF THE ROCK IN JERUSALEM
The Dome of this mosque is covered with real gold.

This is the Dome of the Rock in Jerusalem.
THE GREAT MOSQUE IN MAKKAH
The Great Mosque in Makkah, which contains the KA'ABA, and is the most important place in the world to Muslims. The Ka'aba is the centre of the Muslim religion and most sacred of all places (it is the black square building in the centre of the picture.). The rows around the Ka'aba are the people praying at the mosque.

The Ka'aba contains the Black Stone, the most sacred object in the Muslim religion. All Muslims face Makkah and therefore face the Ka'aba when they pray. Non-believers are forbidden to approach it nor are they allowed in the city of Makkah. Makkah is the holiest city in the world for  Muslims.