Now that the cut down to 53 is behind us, NFL teams will begin establishing their practice squads. Like anything else, the league has rigid rules established by the Collective Bargaining Agreement with the NFLPA explaining how this can be done.
At 12 Noon Eastern time, waivers will clear. Players claimed by a team must be added to that teams 53 man roster. Any player who does not receive a claim then "clears" waivers and becomes a free agent.
After 1 PM Eastern, teams can then extend offers to free agents to join practice squads. Each squad is limited to 10 players.