You can see the extent of his conquest on a map easily enough, but how was his army compiled? Did he have special divisions of foot soldiers, archers and siege engineers? He captured so many cities i can't imagine it was one giant horde of horse archers...
The army of Genghis Khan was organised in tens upwards, with a rigid chain of command.
arban - 10 men with two or three gers between them if travelling fully equipped
jagun - 100
minghaan - 1000
tuman - 10 000
Commanders of 1000 and 10 000 were given the rank of 'noyan'. Above those, men like Jebe and Tsubodai were 'orloks', or eagles, the equivalet of field marshals. Jagun officers carried silver plaques known as paitze and noyans carried one weighing approximately 20 oz of gold. An orlok would have carried one weighing 50 oz.
At the same time, the growth of army organisation, field weapons and messenger routes required a quartermaster type of rank to come into existece. These were known as 'yurtchis'. They chose camp sites, and organised the messengers across thousands of miles between armies The most senior yurtchi was responsible for reconnaisance, intelligence and the day-to-day running of the camp of Genghis.