Hello. ratchet shifters work similar the "retrofriction" shifters touted on here as the best shifters of all time. racthet shifters however make a clicking noise when pulling the lever towards you, shifting into a easier gear in the back/bigring in the front.

both shifters have a type of spring system which creates tension when the shifter is moved toward the rider. this arrangement make the feel of the shifter very light when shifting to easier gears thereby making shifting smoother. the spring inside then holds the shifter/gear rather than pressure applied to the shift lever by a screw and washer. then pushing the lever forward of course release the tension.

this is rather basic, I hope it helps a bit. I am sure there will be dozens of posting later explaining it better and contradicting this one.