It all starts with that little black knob on the lower left hand side below the fairing next to your leg. You can just see the knob to the left of the screwdriver, between the green fairing and the black side cover.
When you turn that knob, it turns a cable inside and the end of that cable screws and unscrews and pushes a lever attached to the carb on the right side.
That plate that the end of the choke cable rotates forward or back is actually the same plate that opens and closes when you twist the throttle, only to a much smaller degree. So, when you increase your idle speed, you are actually raising the throttle plates inside the carb bodies higher to allow more air to pass through the carbs.
The idle speed should be set after the bike is fully warmed up and has been ridden for at least 10 minutes or so. The specs call for it to be set to 1250-1350 rpm. I find it much more simple to just set it to 1500 rpm as it's easier to read it on the tach to set it precisely. You may need to readjust it after a few rides initially, to get it to stay at a constant 1500, but once you get it set correct, the bike should idle at 1500 rpm consistently unless something starts to go wrong with your bike. This is a very good indicator of how your bike is running. Nice steady, consistent idle speed likely means your bike is in a good state of tune. If you see it vary, dip or not hold the same idle speed all the time after it's been warmed up, you should start looking at why.
Dirty pilot jets, carbs out of sync or even bad gas can cause you idling problems. There are many other reasons that can cause this condition, but bottom line is that if you have an idling problem, something needs work on your bike.