What is Fasting in Islam?  And what is the Wisdom behind it?  What is Ramadan?

Ramadan is the name of the Muslims' fasting month.  Ramadan comes approximately every 11.5 months (10 to 12 days earlier every year, because the Muslim month is 29 days except for Ramadan which could be 29 or 30, and February in the normal calendar is almost always 28 days while the other months are usually 30 to 31 days such as July).  So fasting could occur during the summer and during the winter:

Narrated Anas bin Malik:  Allah's Apostle took an oath that he would abstain from his wives, and at that time his leg had been sprained (dislocated). So he stayed in the Mashruba (an attic room) of his for 29 days. Then he came down, and they (the people) said, "O Allah's Apostle! You took an oath to abstain from your wives for one month." He said, "The month is of twenty nine days."   (Translation of Sahih Bukhari, Divorce, Volume 7, Book 63, Number 212)"

The Muslims start the month of Ramadan by sighting the "new moon", which is the crescent as opposed to the full moon, and they end it by either sighting the crescent again, which would appear on either the 29th or the 30th day, or by fasting 30 days.  If the moon for any reason doesn't appear after the 30th day, then Muslims must end their fasting.  The time range is shorter during the winter because the sun sets earlier, hence, making the fasting days shorter.  No drinking or eating is allowed during those times.

The Wisdom behind fasting is to develop self-restraint, feel for the poor, and to fully appreciate Allah Almighty's Holy Gifts to us here on earth from food, drinks and daily comfort.

Developing Self-Restraint, Manners and Discipline is also part of Fasting:

Narrated Abu Huraira: "The Prophet said, "Whoever does not give up forged speech and evil actions, Allah is not in need of his leaving his food and drink (i.e. Allah will not accept his fasting.)"  (Translation of Sahih Bukhari, Volume 3, Book 31, Number 127)"

Narrated 'Alqama: "While I was walking with 'Abdullah he said, "We were in the company of the Prophet and he said, 'He who can afford to marry should marry, because it will help him refrain from looking at other women, and save his private parts from looking at other women, and save his private parts from committing illegal sexual relation; and he who cannot afford to marry is advised to fast, as fasting will diminish his sexual power."  (Translation of Sahih Bukhari, Volume 3, Book 31, Number 129)"

Spouses are also not allowed to have sexual intercourse during the fasting hours.  If a couple do have sex during the fasting hours, then the day they had sex on would not count, and they would have to make it up sometime before the next Ramadan month.  They can eat and drink and live normally during their "invalid" or "excused" fasting day.  If a couple have sex during the valid hours in the sacred month (during the non-fasting hours), then each should wash their entire body (take a shower) to become clean for the next fasting day.  Failing to do so, will result them to become unclean and their fasting would not be valid:

"Permitted to you, on the night of the fasts, Is the approach to your wives.  They are your garments And ye are their garments.  Allah knoweth what ye Used to do secretly among yourselves; But He turned to you And forgave you; So now associate with them, And see what Allah Hath ordained for you, And eat and drink, Until the white thread Of dawn appear to you Distinct from its black thread; Then complete your fast Till the night appears; But do not associate With your wives While ye are in retreat In the mosques.  Those are Limits (set by) Allah: Approach not nigh thereto.  Thus doth Allah make clear His Signs to men: that They may learn self-restraint.  (The Noble Quran, 2:187)"

This rule also applies to the 5-daily prayers through out the entire year as well:  If a couple have sex at anytime during a day, then in order for them to be able to pray, they must wash their bodies or else they would be unclean and their next prayers wouldn't be valid:

"O ye who believe! Approach not prayers with a mind befogged, until ye can understand all that ye say,- nor in a state of ceremonial impurity (Except when travelling on the road), until after washing your whole body. If ye are ill, or on a journey, or one of you cometh from offices of nature, or ye have been in contact with women, and ye find no water, then take for yourselves clean sand or earth, and rub therewith your faces and hands. For God doth blot out sins and forgive again and again.  (The Noble Quran, 4:43)"

Pregnant women, breast-feeding women, and women having menses are excused from fasting, but they have to make up the lost days sometime before the next Ramadan month.  People out of town, and people who are ill are also excused from fasting and they too have to make up the days they missed sometime before the next Ramadan month.  Anyone who can't resist food and drink deprivation during the fasting day can also break his/her fast, providing that they make up the lost day sometime before the next Ramadan month.  If a person can not make up a fasting day after they honestly and sincerely tried, and the next Ramadan month already came, then there are two types:

1-  If a person didn't fast because he/she were traveling or ill, then a "Fidyah" to the poor and needy should be paid for each missed day.  Or you can fast some other day, to make it up, before the next Holy Month of Ramadan.

2-  If the person didn't fast because Fasting was negatively impacting his life (ex: can't fast due to work reasons), or is just not able to fast (after seriously and sincerely and genuinely trying), then a "Kaffarah" of feeding 60 people from the poor and needy should be paid for each missed day if the person can't fast 60 days to make it up.  The person could also free a slave for a Kaffarah:

"....they must free a slave; If not able to: then to fast 60 continuous days; If not able to: then to feed 60 needy people for each missed fast day to their fill or give one Mudd  (= 3/4 kg.) of food-stuff like rice, wheat or barley or bread etc. to each of them." (Source)

Please contact your local Mosque regarding the amount, because it varies from country to country, and state to state, and even city to city, and town to town.  But on average, it is a very small amount that is comparable to a one day of meals for a poor person.  Here in the US, it averages between 8 to 15 dollars per needy person.  Please don't use these numbers as the measuring stick.  It is best if you contact your Mosque.  But as always, the more generous you are to paying for the poor and the needy, the better your deeds will be, insha'Allah (if Allah Almighty is Willing).  And as always, Allah Almighty is the Most Merciful and Oft-Forgiving.