Like ordinary cameras except that instead of film they have a matrix of photocells.
A 3 megapixel camera has 3 million such photocells - probably about 1500 x 2000 pixels. Each photocell measures the intensity of red, blue and green light falling on it. The logic in the camera reads this, converts it into the string of 3 x 3million numbers and stores it in the camera's memory.
Things to consider:
Do you want a camera you can just slip in your pocket?
Do you want a large zoom?
10x zoom great for nature photography but bulky.
Consider only optical zoom. Digital zoom only does what
you can do better in the computer.
How much control do you want?
Point and shoot
Control over aperture, shutter speed etc.
Interchangeable lenses
Image stabiliser - helps prevent camera shake
Megapixels.
For acceptable prints reckon on 200 pixels per inch.
So, a 5"x7" print will need 1000x1400 pixels =
1.5megapixels
An A4 ( ~ 11"x8") will need 3.5megapixels
Remember you will probably want to print only part of the
picture you have taken, so for A4, good quality, go for 5megapixels. You
won't need any more until you get really serious.
Controls.
Can you operate them easily?
Do you want a separate viewfinder?
Is the screen bright enough and big enough?
Cost
£100 - £3000+
Good quality 'snaps' for less than £200.
Storage
Several different types - differences not important - size is
important
Images are compressed so do not need 3 bytes for every
pixel.
However, to get highest quality you may only be able to store
10 or 12 pictures on the supplied memory card.
A 1GB card, good for several hundred images, now costs only
£15.
Reviews
There are lots of in-depth reviews of cameras on http://www.dpreview.com/
and http://www.ephotozine.com
Better quality? Only professionals quibble.
Digitise with:
Film scanner
Flatbed scanner
PhotoCD
Film scanners
Scan negative strips or slides (sometimes small prints)
Best quality (2400lines per inch = 2400 x 3600 pixels on
35mm)
Expensive (~£200)
Or get your images stored on a CD by Boots or Bonusprint
Flatbed scanners
Scans prints (many now scan negatives)
Depends on quality of print
Quite capable of making enlargements
No special requirements
Make sure all your hardware will plug in (e.g. USB ports)
Big images and lots of processing may be slow - get more memory (512MB) before
faster processor.
Most modern printers produce acceptable results, especially those with
'photo' in their name.
'All in one' printers (including scanner and fax) generally not as good as
dedicated ones.
Printing direct from camera card does not allow same control as using a
computer.
Must use decent paper.