RAW files are huge. That's because they are very fine and contain so much more information. For most recreational photographers, though, they're not necessary and you should set your camera to JPEG. Many DSLRs will give you a choice of image resolution too - the lower it is, the smaller the file.
If you have a Nikon, then you need to be aware that their RAW format is different to everyone else's. You can get cheap/free software that will open and/or convert it but not to manipulate it.