How are hourly and salaried gross pay calculated?

If work hourly then you multiply the amount of hours with the rate of the hourly pay and you get what your paycheck should be. If you have a salary, then it's a fixed thing that doesn't depend much on the working hours, but can increase if you have overtime. You won't get all that money though because a part of it goes on taxes and things like that so the money you get is the net pay. Gross pay is without paying taxes and net pay is what remains when taxes are covered.