A picture from a digital camera is made up of very small squares called pixels.
When the picture is fairly small you cannot see the pixels but as you enlarge the picture the pixels start to become visible.
It sounds as though this is happening in your case.
The more pixels on a picture the better.
Cheap digital cameras take pictures at sizes like 640 pixels by 480 pixles (less than 1 mega pixel)
Better digital cameras take pictures with sizes like 2500 pixels x 1700 pixels (about 4 mega pixels).
You need to find out what size your camera is using.
Some cameras can adjust the setting, low quality, middle quality, high quality etc.
Set your camera on the highest quality.
If that is still no good you may need to buy a better digital camera, say a 4 mega pixel or better.