SVG files are vector image files descibed by a text format based on XML. SVG is used for displaying vector graphics on the web. I usually convert them to .ai files and use Adobe Illustrator (Corel Draw works fine too). Vector files can be found all over the internet, and licenses can be purchased from the suppliers. Many free vector files are also available. Some, like those from "Brands of the World", do not include licenses, and you must seek permission to use the files from the copyright owners. You can also vectorize files using Adobe Illustrator (and other programs), but that will not release you from copyright restrictions.
I only cut vinyl for translucent backlit signs, specialty graphics (SignGold, reflective, etc.) window lettering, and some vehicle graphics. For stickers and the majority of signs intended for short term use (most commercial signs) I use vendors such as Sticker Mule and Signs 101. I can't touch their prices doing it myself!