Rather than rewrite what others have said (probably better), I would rather include some links here for sites where you can find information on pet rats.
Some other websites with a huge wealth of information:
Rat Guide – a slightly more medical guide
For something more basic, here is a free printable rat info flyer – click on the image to download the printable PDF or right-click and “Save Link as”. You can also right-click and choose “Save Image as” to download the JPEG, which you are welcome to share online.