Aujourd'hui, ma vie c'est d'la marde talks about a woman who’s boyfriend left her and how she feels like crap after that.

This song uses very informal Acadian/Québec French which shortens many determiners.

“marde” is a way to say “merde” even more informally, which means “crap”. There are even a couple Anglicisms, which are quite common in varieties of Canadian French.