What is Clomid and does it work?

I ovulate regularly and PMS is normal monthly. I'm just not getting pregnant. I had a baby 1 yr ago prematurely at 23 weeks due to an imcompetent cervix. Ever since then we have been trying and its just not happening.. My obgyn has just prescribed me clomid 50mg. I would like to know information, if it works, disadvantages, just anything good / bad on clomid.