'Tain't no use 是甚麼意思？

'Tain't no use意思是沒有用。

It----S
ain't----contracted form of are/is/am/not and have/has not
no use---in negative sense;
useless=of no use---eg:-A car is useless without petrol
It is not no use=It's not useless=sort of "double negative sense";
=useful adj=helpful;producing good result
=eg:-A spade is a useful tool.
=(colloquial) capable, efficient
eg:-He's a useful member of the team of football.
=useful.
However, in vulgar language,ill mannered; in bad taste behaviour eg:-I ain't going;We haven't got any=useless.Thanks.