Why do I need to format a new memory card for a digital camera before using it?

We've have just bought a new digital camera and immediately started taking pictures, then read that the memory card should be formatted before using. What now?

Sometimes the memory cards are pre-formatted, sometimes not (to be honest I highly doubt you'll find one that isn't). When you format it in the camera you just tell the camera to re-write the filesystem on the memory card. The camera will then prepare the memory card exactly how the camera wants the information to be stored.
I remember near the beginning of the digital camera age some cameras would format the card and then the card wouldn't work in other cameras. It was quite a problem when customers would have a few different cameras. I haven't seen this happen in a very long time (3 years or so) so I am fairly certain that all cameras have been designed with very similar standards when it comes to the memory card filesystem.
You may find problems, however, if you use the card in different devices or format it incorrectly in a card reader. I've purposely done this just to see what happens, and it just doesn't work right. So you reformat it in the camera and the camera is happy.

I've done the same thing, and usually it's no problem. Every now and then, the pictures will mysteriously disappear though. Buy an inexpensive card reader and see what's on the card. If you have images there, just transfer them over to your hard drive. Formatting is an easy way to erase old pictures that you've already transferred, but I've gotten by many times by just deleting the pictures using my computer.

its nothing wrong, its just a pre formatted camera. generaly, when a camera is formatted, it creates a new data folder by the name 'dcim' or nikon ... whatever the brand is, to store the pictures for later transfer. as uve already started taking pictures.. . its still fine as i guess it was pre formatted to be used in that camera.