A digital camera stores a picture image on a memory card instead of film. The image on the card can then be downloaded to your PC where you can view, print or e-mail it.
 
Picture resolution and quality
In a digital camera, the picture image is captured in the form of millions of tiny dots or pixels (short for picture elements). The more pixels, the finer the detail of the image which usually means a better quality photo. Most cameras have a resolution of at least 2 million pixels. The more expensive have 4 million or more. The higher the resolution (or the more pixels), the more space the photo will take on your camera's memory card and the fewer photo's you will be able to fit on your memory card. Because of the space, camera's will allow you to take lower resolution photo's.  Typically, you will want to shoot at the camera's highest resolution for large prints but you can use the lower resolutions for snapshots or images that you are going to use in e-mail or on the web.  If you shoot at too low a resolution for the larger photo's, the resulting image will be of poor quality and will look coarse or jagged.  Two to three megapixel cameras provide sufficient detail to print 8 x 10's from uncropped images. You will often need to buy more memory for your camera because you won't be able to fit enough of the high quality photo's on the memory card that comes with your camera.
 
Maximum Print Size
 up to 1 MP: email and web 5x7
 2MP: up to 8x10
 3MP: up to 11x14
 4MP and more: 20x30
 
Pro's
With digital camera's, you avoid the cost of developing traditional film. You can store all of your pictures on your computer disk, thereby saving space and keeping the quality of your negatives intact indefinately. Once on your computer, you can use software to crop, brighten or otherwise improve your pictures.  The LCD (liquid crystal display) let's you review an image seconds after you take your picture, and because the memory card is reusable you can erase any failures and retake the picture until you get one that you like.
 
Con's
Even though you don't pay for film processing you will need to purchase ink cartridges and photographic paper for your printer. Digital camera's are much harder on batteries so you will need to purchase and carry spares for convenience. They can also be sluggish and may hesitate when you try to take several shots in rapid succession.
 
Zoom
Look for an optical zoom of 3X or more. This allows you to frame shots flexibly.  Make sure you get an optical zoom or optical and digital zoom and not just digital zoom because digital zoom is an electronic trick and is not a true zoom
 
LCD
Look for an LCD that tilts or whose brightness you can adjust. This should make it easier to use in bright sunlight.
 
Memory Storage
The memory storage devices that digital camera's use are: CompactFlash, Memory Stick, Smart-Meda, Secure Digital and others. Many camera's come with a minimal storage of 16 MB or 32 MB which will not hold very many photo's.
 
Calculate the number of pictures your camera will hold
To calculate how many pictures your card can hold, divide the capacity of your card by the average file size of your images. For example, if you have a 16MB card and you are using a 3 megapixel camera, your average image file size will be around 1.2 MB.  16MB divided by 1.2 will give you 13 pictures.  For 2 megapixel the average size is 900KB so you will get a few more pictures.  The higher the megapixel's, the bigger the file size.  Most people will find that they need more memory than the minimum of 16 MB.