Can you count? Then you can do this commandment, that is to count fifty days after the holiday of Passover. A medieval spiritual commentary to the Torah named Nachmanides considers these days one long holiday, just like the week of Sukkot or Passover but seven weeks instead. (This year, 2014, from April 15th until June 2nd.) So every spring there are observant Jews counting away, trying to remember which day it is. In fact, its even easier these days with websites, email reminders, and smartphone apps to help you keep track. Like this one for the iPhone https://itunes.apple.com/us/app/ultimate-omer-2-sefira-app/id366802811?mt=8 the 3300 year old Torah meets the modern world.
What's this holiday all about? That's where things get a little bit mystical. Apparently the Israelites in Egypt had gotten influenced by the idolatry around them and had descended to what the kabbalists call the 49th level of spiritual impurity. In order to be holy enough to receive the Torah they had to climb back up the ladder after leaving Egypt. So the Torah was not given to them until they had purified themselves one level at a time, each day, and on the 50th day...boom, the Torah came down, which many have been following ever since. The holiday that marks the last day is called Shavuot, or Weeks, (or Pentecost) emphasizing the importance of the time period that leads to the holiday of seven weeks of counting and spiritual elevation.
So that's it; count away. And, oh yeah, spiritually purify yourself.