Photography

[cintrix]

Ok, I'm really bad with this digital photography so bear with me. What size pixels am I supposed to set my camera to? 1m, 3m, 5m, 6m, 7m ? the 1m is 1024x768 and the 7m is 3072x2304
My daughter has been taking pics with her camera on that 7m mode and when I went to email some of them, the files were so large that I couldn't send them the way I normally do. I had to open them in Picasa - and email it through that - I think they shrink the pics for emailing.

We have three digital cameras and I never noticed that you can change the size. What is the purpose of using the large over the small? Should I be changing the size of this depending on what I am photographing?