Basically, the program runs various tests to figure out the state of your processor and graphics card.
Cinebench is especially useful when evaluating machines with various processors. The newest version is based in 3D animation software from Maxon, called Cinema 4D. The test results will help you know more about your computer's 3D performance.
The package includes a Windows version for 32 and 64-bit, and binaries for Macintosh.