http://www.savingsbonds.gov/Essentially, a Savings bond or "Series EE" Treasury bond is sold at 50% of it's face value and has a 20 year maturity, at which time you receive full face value. All EE bonds have an initial maturity period and an extended maturity period. The initial period is the length of time it takes for the bond to accrete enough interest to bring its value to face value.
Bonds issued after May, 2003 have an initial maturity period of 20 years. If these bonds have not grown to face value in 20 years, the Treasury Department makes a one-time adjustment to bring them to face value. The bond will continue to earn interest until final maturity at 30 years.
It is important to know that there is no secondary market for these securities, which means that they can not be "sold", only "redeemed" by the issuer - the US Treasury. If your time horizon is short, they might not be the best idea.
Other Treasury securities come in various shapes and sizes and this page from the above website will help you understand them;
http://www.savingsbonds.gov/indiv/research/indepth/indepth.htmBills, Notes and Bonds all DO have a secondary market - one of the most active of all bond markets in the world - and therefore you can buy them and sell them at will. Maturities range from as little as 30 days (A "T-Bill") to 30 years (Bonds) and while their interest rate is determined at auction, we hear about their "Yield" changing on a daily basis.
If you are looking for liquidity (something easily converted to cash) and don't mind a modest interest rate, 5 or 10 year treasuries might be something to consider.
It should be noted that most people (with the notable exception of some on DU) can benefit from seeking the face-to-face help of a licensed financial professional.
Hope that helps.