Muslims have 12 months in their calendar and Ramadan is one of those months. In Ramadan all Muslims fast from dusk (approximately an hour before sunrise) to sunset.
Fasting in Islam is not only restricted to the fast of the stomach, e.g. Not to eat or drink all day but also fasting of the hands from harming other people, fasting of the tongue as not to utter any ill or vain talk. Fasting of the eyes as not to see anything forbidden etc.
Muslims see this as a month of gaining control over their ego and Allah (God) tells mankind that for this one act of worship, he will personally reward people on the day of judgement as it’s the one act of worship where people endure hardship to please their lord and there are less opportunities for people to perform this act of worship to show off to other Muslims their piety, in order to gain their praise.
The rewards for almost every good deed and act of worship is multiplied many folds in this month and thus we see Muslims giving a lot more in charity and performing lots of other acts of worships usually not done so on ordinary days, in order to bulk up their good deed account with god.