Newbie Protection, or Beginner's Protection, is the period of time new players are protected from attacks. The exact number varies depending on how long the game has been running. It starts from a minimum of three days and can be as long as two weeks, perhaps even longer.
It's recommended that a Cranny be built before Beginner's Protection ends, as this protects specific amounts of resources from raiding. (There's another big advantage in building a Cranny fairly early - you get free gifts from the tribal headquarters. Quoting from elsewhere in this wiki: "build it soon after coming online, because you get a free delivery of 125 units of each resource then and 6 hours later and 12 hours later, and you will want to be online soon after those deliveries so as to use the resources. Before building the Cranny, ensure that none of your resource amounts are much over 600, or you may waste some of the first delivery as they take your amounts over the Warehouse or Granary size.")