When college players are drafted into the NHL, they will often play one or two years at that level before signing a contract with the team that owns its draft rights.
However, if a player decides to stay in college for the full four years of his career, a different set of options opens up. The drafting team has the rights to the player for four years. But if he does not sign with that team, he becomes a true free agent and can work out the best deal with any team willing to employ him.