Working principle of the reverse gear shaft

It has three shafts: the first is the primary shaft, connected to the clutch, which is the input shaft and has six gears for five forward gears plus reverse gear; the second is the secondary shaft, which has six sliding gears, each of which meshes with a gear on the corresponding primary shaft to produce the transmission of five forward gears and reverse gear; the third is the reverse gear shaft, which has one gear that meshes with the reverse gear.