Developing photos? Came out pixelated?

So i own a nikon d5100, i used it to get a family photos of my kids and i. (using raw files) when i finished i went to walmart to printout the photos i took through USB. Then when it came out it was pixelated so bad that i can even recognize our faces. So my question is does it need to be in jpeg format? How can i get the best quality when prinnting/developing photos for portraits?

You generally need to digitally process the files if you shoot RAW. Load them in your computer, use Nikon's software to tweek and sharpen the photos, crop them to the size you want, and then develop them as high quality JPEGs. Then get the JPEGs printed.