The Washington Post has a good article about it here. One man they interview says,
"It's about abstaining from the feeding of one's passions. The whole personality is fasting. The mouth is fasting from improper speech. The ears are fasting from hearing speech that is not appropriate. Our eyes are fasting from looking at things that might arouse us even if those things are permissible under normal circumstances."
It's not meant to be a time of hardship or torture, but rather a time of spiritual awakening. People do eat before dawn and after sunset each day. And people who are feeble, sick, pregnant, nursing or traveling are exempt from the fasting.
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Photo above is by Naser