theory

Yeah there's four volumes:

Volume One published 1867 and revised three times before Marx's death. This is the one Marx expected people to read and is edited for readability, clarity, consistency, style, etc. This is the best book ever written by anyone ever.

Volumes two and three were published after Marx's death, by Engels. They are edited mostly from a single manuscript each iirc, both written before the publication of volume one. These ones are not ones Marx expected people to read, and it is barely edited at all (and not edited for readability, clarity, consistency, style, etc). These ones are alright, but barely readable in large sections even by nerds.

Volume four is the historical part where Marx details the history of the various schools of political economy, published after Engels' death by Kautsky It is a very good demonstration of how to criticise political economists; unfortunately, as Marx learnt later in life, if you criticise the political economists hard enough (and the bourgeois gain enough political power) they will stop even trying to make sense and invent marginalism.