Does emergency contraception such as Plan B or Next Choice work?

my boyfriend and i had the other day. unfortunately, the condom broke and he already d inside me. after finding this out, we heard of a pill that a woman can take if such a thing happened that would prevent pregnancy from occurring. we went to the local pharmacy and bought Next Choice. i took the first pill about half an hour after we had and took the second pill 12 hours after ingesting the first pill as directed. so now we wait. i was wondering if this is as effective as they say it is. as you can imagine, my boyfriend and i are scared about this whole thing so some good news and further input would definitely ease our minds. thanks.