The Russian Orbital Segment of the ISS contains six modules.
Those modules are Zarya, Zvezda, Poisk, Rassvet, Nauka, and Prichal. Together they form the Russian-operated portion of the station and provide functions including habitation, docking, storage, propulsion support, and spacecraft control.
Zarya was the first ISS element, launched in 1998, and initially supplied power, propulsion, and guidance. Zvezda followed in 2000 as the main Russian service module and became the central living and control area for the segment. Poisk and Rassvet provide additional docking and research capabilities, while Nauka is a laboratory module and Prichal is a nodal docking module.
A common mistake is to count only the older core modules or to confuse modules with all Russian hardware and attached equipment. The six-module figure refers to the current composition of the Russian Orbital Segment itself, not every spacecraft or structural component associated with Russia’s ISS operations.