>>64114410
>Is the Imperium made up of smaller factions of unique groups or some shit.
Yes. There are many different factions within the imperium that often have their own, sometimes directly conflicting, goals. A few of them off the top of my head.
>Local planetary defense forces
The national guard equivalent, with variations for basically every culture imaginable.
>The Imperial Guard
The space army. The "default" ones are "Cadia flavored", but there are a billion different flavors of soldier. Basically one for every IRL army ever.
>The Imperial Navy
The space navy (transports the space army, but also does their own space fight stuff)
>The Mechanicus
Provides tech support and maintenance for everyone, but also has their own independent army and navy
>The Ecclesiarchy
The space church. Also has their own independent army and navy
>The Administratum
Space bean counters. They do logistics with varying degrees of success. They don't misplace the records for too many star systems.
>The Space Marines
Giga nigga super soldiers. Bunch of different flavors of them. All of them operate independently with their own goals and objectives.
>The Inquisition
Space Glow-niggers. They do what they want and have a shit ton of authority.

All of them are officially united together, but how closely that they'll work together can vary a shit ton. It can run the entire gamut of one chapter of space marines moving heaven and earth to try to save every last man, to them slaughtering an entire friendly planet's population to prevent the risk of information spillage.