Every team gets to protect a certain number of players -- X number of forwards, Y number of defensemen, Z number of goalies. There is usually some choice in the matter -- ie, if you can pick a larger number of forwards and fewer defensemen, or something. There are also usually rules about what kinds of contracts must or can't be protected. And then the expansion team gets to go through and fill out a roster by taking one unprotected player per team.
In the past NHL expansion has allowed teams to protect enough good players that it's taken all the expansion teams forever to get going, because all they've been able to start out with are bad players and bad contracts. This time they apparently want Vegas to be a viable team as quickly as possible, so I think I read that just about every team is going to have to expose at least one top-six forward or top-four defenseman. And I don't think you can protect two goalies. It's gonna hurt.