There are two softwares available now. I use Sure Cuts Alot
Here is the company site.
http://www.craftedge.com/index.htmlThis is a third party site that sells it, I would trust this site. (they also sell the other program, which I am sure is good, SCAL was the first and what I own)
http://www.scrappingtable.com/home.htmlYou need a USB cable to connect the Cricut to the computer, basically a printer cable. You start by connecting the Cricut, going to the Cricut website and updating the firmware on the machine. I purchased the downloadable version of the software, you are sent a serial number, they keep it on file. I had to reenter my info once and the company had it.
Once installed, you are ready to go. You can cut any font, SCAL, and SVG files. SCAL are ones you make with the software, I haven't even gotten into that. SVG are vector files. You can make you own. However, both are readily available for free all around the web. There are many sites that sell cutting files and sell the SVG versions. I have tons that I have gotten free. it is a problem, seriously.
One of my favorite things, you see the cutting mat on your monitor. You know exactly how tall and how wide your items are going to be. You can adjust the size to fit on your page perfectly. I have not used a cartridge since buying the software.
Technically, using this software voids your machines warranty. But it doesn't DO anything to the machine, it is a computer program. If your machine is older than a year it doesn't matter anyway.