Command is a selectable multiplayer gamemode in Uncharted 4: A Thief's End. The main goal of a command match is to capture three command sites, to get points, or defeat enemy captain, for bonus points. The first team to 700 points wins the match. It replaces the gamemode: Turf War from Uncharted 2: Among Thieves and Uncharted 3: Drake's Deception.
There are a number of Command Sites across each map. When your team captures one, your team’s score will increase. Command Sites captured by the enemy team must be neutralized before you can capture them for your side. Command Sites are captured faster when more members of the team are inside them.
Whichever player contributes the most points to the team’s objective is the Team Captain. The Captain will receive bonuses — cheaper In-Match Store Items, the ability to revive teammates faster, and more health when downed. When a Captain is designated, the Captain starts at Level 1, but as the Captain gains objective points without being KO’ed, the Captain goes up a Level to a max level of three, which increases the effectiveness of the Captain bonuses. However, at higher levels, the Captain is more visible to the enemy:
Level 1: Enemies see a Captain icon by the Captain’s name
Level 2: Enemies can always see the Captain on radar
Level 3: Captains are automatically Marked until they lose Captain status
Captain status is lost when the Captain is knocked out, which scores the enemy points depending on the level of the Captain. This mode can have some intense comebacks given the large point value a Captain can reach. 
-PlayStation official description for Command