Will an intrauterine device stop an std?

No. An intrauterine device prevents pregnancy. It does not prevent infection with a sexually transmitted disease.
No. No, an IUD is implanted to help try to prevent pregnancy. It has nothing to do with trying to prevent std infections. It has absolutely no effect on risks of getting an std. Also, having an IUD inserted may actually increase the risk of obtaining an std, particularly within a few weeks of impantation. Overall, women at high risk for stds are to be cautioned about the risks of iuds and stds.