Click on the title of the game you want to play and then go down and select "Begin Game".
If it asks you to register, just click "maybe later" and it will take you directly to the game.
http://www.iknowthat.com/com/L3?Area=FractionGame
I recommend starting with one of these games:
Fraction, Name, and Picture Match
Fraction and Picture Match
Equivilant Fractions and
Adding Fractions with Same Denominator