3rd Gear

Hydraulic pressure is applied to the 3rd clutch, then the 3rd clutch engages the secondary shaft 3rd gear with the secondary shaft.
The mainshaft idler gear drives the secondary shaft via the idler shaft idler gear and secondary shaft idler gear.
The secondary shaft 3rd gear drives the countershaft 3rd gear and the countershaft.
Power is transmitted to the final drive gear, which in turn drives the final driven gear.

Fig 1: 3rd Gear Power Flow Diagram
Courtesy of AMERICAN HONDA MOTOR CO., INC.