For SCJP exam, you need to know only that strictfp is a keyword and can be used to modify a class or a method, but never a variable.
Marking a class as strictfp means that any method code in the class will conform to the IEEE754 standard rules for floating points. Without that modifier, floating points used in the methods might behave in a platform-dependent way. If you do not declare a class as strictfp, you can still get strictfp behavior on a method basis, by declaring a method as strictfp.
