This is indeed one of FAQ on the Vikings. While I'm willing to post additional answer to follow-up questions (but probably not within 12 hours due to the real time issue), you can check one or more of the following relevant threads and their posted answers before:

• What stopped the viking colonization of america? by /u/textandtrowel
• Did the Scandinavian people know about Vinland? by /u/sagathain and me
• What knowledge did mainland Europeans have of Iceland, Greenland and Vinland during the Middle Ages? by me.