Ramadan is the name of the Muslims' fasting month. Ramadan comes approximately every 11.5 months (9 to 10 days earlier every year, because the Muslim month is 29 or 30 days and February in the normal calendar is 28 days with 29 days in every fourth year while the other months are usually 30 to 31 days). So fasting could occur during the summer and during the winter:
Narrated Hazrath 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. So he stayed in 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."
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.
Muslims fast simply because Allah Almighty commands them to do so. We fast from sun rise to sun set. The time range is shorter during the winter because the sun sets earlier, hence, making the fasting days shorter. No drinking, eating or sexual relationship 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 Manners and Discipline is also part of Fasting:
Narrated Hazazth 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.
Narrated Hazrath Alqama: "While I was walking with Hazrath 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 committing illegal sexual relation; and he who cannot afford to marry is advised to fast, as fasting will diminish his sexual power."
Spouses are also not allowed to have sexual intercourse during the fasting hours.
"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)"
"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.