Here is a good video a stride:
http://www.youtube.com/watch?v=Qgf6Y_NXVkA
The speed of this particular stride is unimportant. He's Bolt, so it's probably fast. But you get the idea. He's in full sweats, he's walking around, relaxed, then it's just a short but fast run to get him warmed up. So strides are usually done as part of a warmup OR after a run just to get the legs moving faster.
It's usually a short distance, I like 100 meters but 150's or 200's are fine. The important points are (1) to go fast but not too fast, maybe mile race pace (2) to do this with good relaxed form (3) to not tire yourself out with these. Take long rests and don't do a million of them.