There are many different subjects for the trivia - from English grammar to languages to mathematics to the Periodic Table of the Elements. There is a little something for everyone and the best part is that there are different levels to the trivia, so anyone and everyone can answer these questions.
Here is a quick little video I found from the FreeRice website, which explains, in a nutshell, their program.
You don't have to be registered to play - you can play as a guest. Registering only means that you can keep track of your totals for donations.
In total, 94 642 292 420 grains of rice have been donated. As of January 3, 2012, one million people were registered on FreeRice. Will you be one of them?