The NHL's annual free-agent signing period begins at noon ET on July 13. While unrestricted free agents can sign with any team, a restricted free agent can only change clubs if he is traded, doesn't receive a qualifying offer (thus making him an unrestricted free agent) or signs an offer sheet from a rival team.
The player informs his current team once he's signed an offer sheet, giving it seven days to match it. If the club doesn't match it, he is free to join his new team, while his former squad receives a predetermined number of draft picks as compensation.