I've written two web pages with which you can practice with converting numbers in standard form.
The first page gives you a number which you should convert to standard form. There are a few bugs in the program which I will fix shortly. If you get a very long number, pass on it, as it is a computer error and is impossible to get correct.
The second page asks you to convert back from a number in standard form to normal numbers (page only works in Internet Explorer).
You should have had an introduction to scientific notation before attempting these pages.