The P3/P4 truss assembly was installed by the Space Shuttle Atlantis STS-115 mission, launched September 9, 2006, and attached to the P1 segment. The P3 and P4 segments together contain a pair of solar arrays, a radiator and a rotary joint that will aim the solar arrays, and connects P3 to P4.
The P5 and S5 trusses are connectors which will support the P6 and S6 trusses, respectively.
The P6 truss was the second truss segment to be added, because it contains a large Solar Array Wing (SAW) that generated essential electricity for the station, prior to activation of the SAW on the P4 truss. #iss_modules