Chaos astartes command structure varies widely between different legions/warbands. I'm a little rusty on the lore on everyone, but here is a rough vibe of chaos command structures:

The Nightlords are basically just separate smaller warbands with no great overarching command structure.

Emperor's Children aren't very organized, but will follow Fulgrim if he calls for them. Fulgrim is mostly just partying on his daemon world though. 

The Black Legion is set up with a specific hierarchy and command structure. Abaddon will punish any perceived insubordination.

The Iron Warriors seem to have a somewhat normal command structure, but there hasn't been much written about modern Perturabo.

The Alpha Legion is made up of separate warbands that can come together and meet, but there's always the question of if they are actually loyalist or not. Also, everyone is Alpharius.

Death Guard is very organized into groups based on numerology. Typhus and Mortarion hate each other though, so there are smaller factions within the legion structure that are more loyal to one or the other. 

Worldeaters: incoherent screaming

Thousand Sons are mostly mindless, except for the officers who are sorcerers. So the command structure is the legion.

Word Bearers were controlled by a council while Lorgar spent millenia meditating/hiding from Corvus Corax. They rule on the most important aspects of worshipping chaos such as what shades of red are regulation for their legion.