To explain how it works, I'll use the decimal system, since it is something we're used to. For starters, we could multiply all numbers by 100. Note that the answer is 275, and not 2.75. If we want to display the result to the user, we'd have to divide it by 100 to get back to floating-point land. This process of multiplying floating point numbers to get integers is called shifting.
Subtraction works just like addition, but multiplication is a bit trickier.
When dividing, the problem is that we get a result that is 100 times too small. As the table shows, fixed point has a clear advantage when adding or subtracting, being as much as twenty times faster at adding two numbers. Division is not quite as fast, but still twice as fast as its floating-point counterpart. The real hog is multiplication, which manages to be actually slower as fixed-point. As an example, I'll use Fractals.