Ramadan takes place during the ninth month of the Islamic calendar, the month in which the Koran is said to have been revealed to Mohammed by the angel Gabriel.
For Muslims, it is a month of strict dawn-to-dusk fasting.
For details, you may see Submission.org's Ramadan, Ramadan on the Net, the Ramadan Awareness Campaign -- do an Internet search, and see what you come up with -- and, of course, Wikipedia has articles on Ramadan and the month of Ramadan.
Ramadan this year corresponds to the month of September.
I wish you all the best this Ramadan. :)