Brown was notified of the move in a letter from Adolpho Birch, NFL's Senior Vice President of Labor Policy and League Affairs. In the letter, Birch goes over some of the guidelines Brown must adhere to under the Commissioner Exempt List.
While on the list, Brown cannot practice or attend games, and is allowed at the Giants' facility for meetings, individual workouts, therapy and rehabilitation and other permitted non-football activities if permitted by the franchise. Brown will continue to receive his normal salary and will be eligible for all the benefits he qualifies for under the Collective Bargaining Agreement.
Here's a full description of the Reserve/Commissioner Exempt List directly from the NFL Player Personnel Policy Manual:
The Exempt List is a special player status available to clubs only in unusual circumstances. The List includes those players who have been declared by the Commissioner to be temporarily exempt from counting within the Active List limit. Only the Commissioner has the authority to place a player on the Exempt List; clubs have no such authority, and no exemption, regardless of circumstances, is automatic. The Commissioner also has the authority to determine in advance whether a player's time on the Exempt List will be finite or will continue until the Commissioner deems the exemption should be lifted and the player returned to the Active List.