What if your image looks cheap and grainy? Assuming it's not a flaw in your expensive camera, it might be due to taking a shot in low light.
Your camera will automatically do its best to make a good exposure in low light, and the most common way is for it to fire the flash. But maybe you told it not to fire the flash, so it has to do something else.
"Oh, I know," the camera says, "I'll increase my sensitivity to light."
In effect, the camera is able to "do more with less", by sampling light for a shorter time, and simply being more sensitive to it. (This is known as "increasing the ISO".) This additional sensitivity, however, comes at a price.
As you might have guessed, that price is additional graininess. If you want more graininess, increase the ISO or lower the light on your subject. If you want less graininess, decrease the ISO or raise the light on your subject.
There is one more thing that can cause graininess, and that's the level of compression used on the image. See the section on JPEG Jaggies.