Hiya, the fact that they are 10 and 245 confirms there is something there - if you were to print them for instance the 245 should show the faintest of tones against pure white paper. You might want to check your monitor to confirm that the brightness and contrast are not set too high - here's an example of 245 and pure white- you should be able to see a clear difference -

As for stops - it's a bit of an antiquated term but is still used all the time. A whole 'stop' refers to a doubling or halving of exposure - depending on which direction you make the adjustment. Most cameras also offer you the option to adjust exposure by a third and a half of a stop. It can be achieved with the shutter or the aperture control.

Garry