What's the function of 'choke'?
For that, you'll have to understand the working principle of an engine first.
In simple words, a 4 stroke internal combustion engines has following FOUR cycles:
1. Piston goes down and sucks air and fuel in the cylinder.
2. Piston goes up and squeeze the fuel air mixture.
3. Now spark plug does its job and ignites the mixture to form an ignition.
4. Now, what happens when you ignite petrol? It burns, right? And when fuel is compressed with air, it BLOWS UP like a BOMB! Don't worry, it doesn't hurt the engine as the explosion is tiny! The explosion pushes the piston down which turns the crankshaft via the gear box. And the same process repeats again and again and again and... Until you turn-off the engine!
Now, what choke does?
A cold engine is pretty hard to start-up because fuel turns into gel overtime. Hence, to start an engine easier, choke allows more FUEL to get in the cylinder as more fuel rich mixture is much easier to ignite for the engine!
Since you're asking so many question about your bike, I thought you might be a little interested about how engines work...
Hope it helps,
Mr. Nine.