Fate/stay night is a Japanese visual novel developed by Type-Moon, which was originally released as an adult game for Windows.
The original Fate/stay night anime series aired between January 6 and June 16, 2006, containing 24 episodes.
Now you can see what is the viewing order for fate related works:
There are 6 titles of Fate/ anime (yahoo answers talk):
1. Fate/stay night. Fate/stay night(the first anime) is based on the visual novel’s main arc or the “Saber Arc”, it is a 24-episode anime.
2. Fate/stay night TV Reproduction. Fate/stay night TV Reproduction is just a shortened version of the series and is only a 2-episode OVA.
3. Fate/stay night: Unlimited Blade Works. Fate/stay night: Unlimited Blade Works is a movie covering the alternate arc of the visual novel or the “Tohsaka Arc”, you should remember that this is an “alternate” story than the first tv series.
4. Fate/Prototype. Fate/Prototype is the author’s original story even before the visual novel was published, it is only a 1-episode OVA, it has no direct relation to the other titles.
5. Fate/Zero. Fate/Zero is the prequel to the Fate/stay night anime and consists of 13 episodes.
6. Fate/Zero 2nd Season.