This has been covered and therefore I shall close this since a simple search could have answered your questions, but I will give you a brief synopnis.
Briefly, rails are sources of power your computer draws at rated a voltage (3.3v 5v or 12v) with a specific output and current rating for specific components. Read this
for a more extensive explanation.
In short, timings refer to nanaseconds memory takes to refresh from a cycle. I cannot stress enough that timings effect stability, not bandwidth, and therefore are only important if one intends to overclock.
For anything you could possibly want to know about timings you should read this