I don't know nothing (anything) about this car?意思

I don't know nothing (anything) about this car?意思
经常看到I don't know nothing about this car?这句话,
为什么不说 I don't know anything about this car?这两种说法有什么区别?是肯定的说法还是否定的?也有这种说法It is not gonna do you no good doing this.肯定还是否定的啊?
请来点专业的回答 这是 一些很口语的说法
希望有口语方面 优秀的人士来作下地道的 表述，
这两种说法 好像是一样意思的！