This is a big topic, and not without controversy, so you might want to search the forum for "Monosoupape" (note the spelling); but briefly, here goes:
Like most internal combustion engines the rotary engine was controlled by adjusting the flow of fuel and air into the cylinders. Loosely speaking, if you let in more fuel, the engine runs faster.
In most rotaries (including the early, pre-Monosoupape Gnomes) this was done by giving the pilot two control levers, one for the petrol and one for the air, which altered the flow into the carburettor (which the engine certainly did have). The "throttle" is the air lever. In theory you could adjust the positions of the levers to give a range of engine speeds. In practice this was tricky to achieve, for several reasons, and most pilots seem to have relied on just a couple of settings: idling, and full speed. Pilots were taught to land with the fuel supply cut off completely, because it was much too difficult to land in the modern way, with the engine running but constantly adjusted.
The Monosoupape was (partly) an attempt to make all this simpler by giving the pilot just one lever, to control the petrol. The air flow was effectively fixed. Unfortunately, because of the way a rotary works, this made it difficult to achieve any setting other than full speed.
The purpose of the blip switch was to cut off the electricity to the ignition system, which of course stops the engine from firing. It suffered from several disadvantages. The switch itself was not always reliable (as Cecil Lewis
, for one, found out the hard way) and could give you an electric shock. Its use was regarded in some circles as unprofessional. It was strongly discouraged while in flight, because the propellor would continue to windmill round, and the engine would therefore keep sucking in oil, petrol and air, and blowing the unburned mixture out of the exhuast valves. This could lead to oil deposits fouling the spark plugs, which then might not work when you released the blip switch; while a build-up of unburned mixture under the engine cowling could start a fire.
For all these reasons the blip switch was mainly used to keep the speed down while taxying. This is said to produce a characteristic on-off engine noise. However, it is also the case that an idling rotary may misfire on some cylinders, producing a similar sort of noise.
This lack of control was not seen as a problem in the heyday of the Mono engine (say, 1914-16) because formation flying (which requires constant small adjustments to the engine speed) was not much practised. When formation flying became essential, engine design changed. Later rotaries often had adjustable ignition systems, enabling the pilot to select the number of cylinders that would fire, and hence to control the engine speed. They also seem to have been better tuned to allow a range of fuel-air settings to be found, at least while you were airborne and well away from the ground.
Hope this helps. No doubt others will correct my mistakes!