Small tape worms and my dog?

I finally got a dog that I love she is a 7 month old lab mix. I realized after roughly a month of having her that she has small tape worms they are the little rice or maggot looking things by the and in the fecus. I have a couple questions, 1 how did my dog get the small tape worms 2 Is there anything at a grocery store that I can buy to get rid of them 3 could my dog die from this? 4 I have a two year old, I am keeping up with this dog the best I can due to she is not fully trained yet could these tape worms harm my child?