The leap month is named Adar II (Adar is a regular month, that generally happens in February-March), and is inserted after the regular month of Adar. When we do that, as we will do in 2011, there’s Adar I and Adar II. Passover generally falls late when we have a leap year, since Passover is in Nissan, the month after Adar or Adar II.
Jewish years go in a 19-year cycle. We insert an extra Adar into years 3, 6, 8, 11, 14, 17, and 19 of the cycle. Year 19 is a year evenly divisible by 19 (the year number is the Jewish year number, not the regular year number) The current Jewish year is 5771, which is year 14 in the cycle. The Jewish year starts at Rosh Hashanah, so we just started a new one.
We also vary the lengths of some months, a la the Gregorian calendar’s method of doing leap years. But that’s mostly to keep holidays falling on the right days of the week. The calendar is set up so that Yom Kippur can’t fall on Friday or Sunday, because if it fell on Friday, you’d have trouble preparing for Shabbat on Saturday, and if it fell on Sunday, you’d have trouble preparing for Yom Kippur on Shabbat. There’s also a restriction that Hoshanah Rabbah can’t fall on Shabbat. Hoshanah Rabbah is a holiday that was a much bigger deal when they were setting up the calculated calendar than it is for most Jews now.
In practice, most of us buy a Jewish calendar, or Google for when the holidays are. I have a book that has the dates of all the holidays from 1900 to 2100.

