I think you're refering to the Bi-Annual flight review...
As a private pilot you do need a bi-annual flight review every 24 months. This means going up with a CFI for a minimum of 1hr and doing a minimum of 1 hr of ground. Keep in mind that 1hr is a minimum and that the CFI has to work with you in areas that he/she sees you as being deficient.
Don't forget to have the CFI endorse your logbook!
One way you don't have to do a bi-annual is by getting a new certificate or rating. Basically any check ride given by the FAA will count (multi-engine, instrument, commercial, CFI etc.) An endorsement (complex, high perf, tail dragger) does not count.
Keep one thing in mind, the BFR is NOT a pass or fail event. A good CFI wil treat it as an opportunity to help you in any areas that you need help in. This is what the FAA intended it to be. The CFI should review your log book, this will tell them alot about your experience and give them an idea on what to cover in that hour of ground and hour of flight review. I would recommend that you have some definate ideas on what you want to cover. If you haven.t done stalls or slow flight for a while, it is a great opportunity to review them. If you are thinking about upgrading your rateings, ask them to take you out and demonstrate either a new maneuver or maybe an ILS. Realisticly you will spend much more than 2 hours with the CFI but it is worth it to both of you. I believe that the many BFR's that I have given have been a very good experience and actually been fun. Relax and enjoy after all you are getting to fly.
"...and that the CFI has to work with you in areas that he/she sees you as being deficient.
This is not literally true. The BFR gives both the pilot and CFI a lot of leverage in the absence of requirements. If someone comes to me and says, "you know, I aint done a power on stall in 30 years... but what I am REALLY afraid of is soft field takeoffs in that 235HP Cessna RG", we can go out and do JUST that for an hour.
In practice, my "expectations of proficiency" so to speak are a lot more lax on the BFR than doing an insurance checkout for a renter.
Two extra comments on the BFR's, and I have done a BUNCH in the past six months: 1) when I meet with someone and the first thing outta their mouth is how many hours they have and all that they have done blah blah blah.. WATCH OUT. These guys have surprised me with the things they do to me in the airplane, and 2) the best BFR's I have conducted were with people (with 100 hours, 10,000 hours.. dont matter) who treated it like a ride that they could fail!!
Biannual= two times a year. Biennial=every two years. Not important though. As a private pilot, in order to log PIC time you do need a Biennial flight review. It is, as the others said, an excellent time to ask a CFI to review something you werent sure of, or to try something new in the air! ENJOY!