Custom widget using svg files

[Hogwarts]

I want to develop a custom widget that will use svg files, to improve its design quality, for example a tank level signaling, of course using QtSvg Module...Now, I'm new using svg files, so I dont't know how to create it. I want to know if there is any application to create svg files, or if I have to create them myself??
on the other hand any sample code of a custom widget that use svg files, be well received
thanks
excuse my English!