classic motorcycle forum

Hi, I'm a novelist working on a book set during WWI and I'm interested in Royal Enfield motorcycles of the era.  I know that Enfield supplied 225cc and 425cc bikes to the British Army.  I've never ridden a motorcycle and I'd like to know how bikes of this era were operated--eg, how did you start one, how did the throttle, brakes and gearshift operate, etc.  It's pretty tough describing something you know nothing about, even for a few sentences.   Can anyone recommend any sources for this, or have firsthand experience?  

Many thanks!