General fluid intelligence applies to tasks where one must integrate new information, notice novel patterns in stimuli, and draw reasonable inferences without the benefit of domain specific expertise that might allow one to merely retrieve a learned correct answer from memory.
IOW, it is very general, however, that does not mean that it is the sole or even primary determinant of most cognitive performance. It has to do with how easily one learns given X amount of instruction or exposure, but give a person twice as much exposure and they will learn more than a person with higher general intelligence. Also, the more the task relies upon highly specialized knowledge or execution of physical movements/manipulations, the less influence general intelligence has.