Why do we fast in Ramazan?

It is from the nature of humans to ask and to wonder why they do things. Muslims do things to please Allah, and they can please Allah only by obeying Him and practicing His religion. Thus, in answer to the question some ignorants may ask "Why do we fast ?" we respond that it is a commandment and a clear order from Allah upon us and we have no other choice by to obey Allah and Please Him out of Love and Fear at the same time.
Allah says in the meaning of : "O you who believe, fasting has been prescribed for you as it has been prescribed for people before you so that you will (learn how to) attain Taqwa" (Qur'an, al-Baqarah, 2:183)
Ibn 'Umar reports that Allah's Messenger said: Islam is based on (the following) five (principles):

1. To testify that none has the right to be worshiped but Allah and Muhammad is Allah's Messenger.
2. To offer the (compulsory congregational) prayers dutifully and perfectly.
3. To pay Zakat (i.e. obligatory charity) .
4. To perform Hajj. (i.e. Pilgrimage to Mecca)
5. To observe fast during the month of Ramadan. [Bukhari]

What is Ramazan or Ramadan or Ramzan?

Ramzan is the ninth month according to Islamic Lunar calendar. Ramzan (written as Ramadan) is derived from the Arabic root word 'ramida' or 'arramad' that means intense scorching heat and dryness, especially of the ground. Ramadan is so called to indicate the heating sensation in the stomach as a result of thirst. Others said it is so called because Ramadan scorches out the sins as it burns the ground. Some said it is so called because the hearts and souls are more readily receptive to the admonition and remembrance of Allah during Ramadan, as the sand and stones are receptive to the sun's heat.

Ramadan begins after the month of Shaban, after the new moon has been sighted. In case new moon is not sighted then after 30 days of Shaban, Ramadan begins. The month of Ramadan lasts for 29 or 30 days depending on the sighting of the moon. If the moon is sighted on the night of 29th fast then the month of Shawwal begins from tomorrow and Ramadan is over. The 1st of Shawwal is the Eid also know as Eid-ul-fitr to distinguish it from Eid-ul-azha (Bakri Eid).

Ramadan is the month in which the Quran was revealed. The Quran clearly says "O you who believe! Fasting is prescribed to you as it was prescribed to those before you, that you many learn piety and rightousness" - Al Baqarah, 2:183. Fasting is to be done by all able bodied men and women and children who have reached puberty. If a person is sick or has some medical reason or if a women is pregnant then they are waived from fasting.

During Ramadan the people who fast are not allowed to eat or drink anything (including water) from dawn to after sunset. Also one has to restrain other body parts, which may render the fast worthless despite the main factor of hunger and thirst; so the tongue, for instance, must avoid backbiting, slander, and lies; the eyes should avoid looking into things considered by the Lawgiver as unlawful; the ears must stop from listening to conversation, words, songs, and lyrics that spoil the spirit of fasting; and finally restraining of the heart, and mind from indulging, themselves in other things besides zikr or Allah (remembrance of Allah).