This is the Jumeirah Mosque in Dubai, United Arab Emirates.
At certain prescribed timings during the day, Muslims everywhere are called to prayer by the "Mu'athin" in the Mosque. There are 5 daily prayers- the "Fajer" or Dawn prayer; the "Dhuhr" or Noon prayer; the "Asr" or Afternoon prayer; the "Maghrib" or Sunset prayer; and the "Isha" or Night prayer.
A Mosque is where Muslims can congregate to perform the 5 daily prayers, and although praying at a Mosque is preferable, it is not necessary; it is permissable to pray alone or in a group at another place.
Prayer (or, in Arabic, salaah) is one of the five pillars of Islam and, as seen by Muslims, is the symbol of worship. It is an action specifically ordained to be performed in a certain way at particular timings during the day.
Muslims see that it is the action of prayer that connects one with God regularly and breaks off the occupation with the world. Salaah is performed in gratitude, reverance and love for God.
Another form of prayer or supplication is called "Du'aa", which has no prescribed method or specific timing for it. It is asking or talking to God.