To sing you must first open your mouth. You must have a pair of lungs, and a little knowledge of music. It is not necessary to have an accordion, or a guitar. The essential thing is to want to sing. This then is a song. I am singing.
I'm regularly asked, 'What's a good voice?' I often answer, 'One that I don't notice'. I would also add, one which makes me notice things about a spoken text