It means something is cheaply made, of bad quality, or not a branded product. Ex.
This car sucks. It has broken twice since I bought it, and that was a monthy ago.
Esta carro esta muy chafa. Se ha descompuesto dos veces desde que lo compre, y eso fue hace un mes.
I hope you have learned something new, about the spanish that real Mexicans talk on their everyday life.
If you want to improve your Spanish, I also give tutoring lessons on skype using this page that host many teachers from all over the world, and while I don’t really do grammar, I can help with conversation and doubts about the language. Also, if you are interested in any language besides spanish, there are teachers and tutors for any language there.