There are many threads here about carb tuning. A plug chop is simple, it means, while riding, chopping the power (hit the kill switch and pull in the clutch) while running the engine at the performance point you're trying to tune and then coasting to a stop and removing one or more plugs for inspection. The plug colour and condition will tell you if the engine is running lean or rich (withing a pretty broad range). For carb tuning after engine, exhaust, or intake mods you start with wide open throttle at mid to high rpm and get the main jet size correct. Then you move down the throttle range and get the needle position (and taper if you have an assortment of needles or are willing and able to modify yours), slide cutout (if you have an assortment of slides or are willing and able to modify yours) and pilot jet/metering screw settings correct.
Modern practice is to do this on a dynamometer with exhaust gas monitoring, you can get much more precise measurement of mixture this way. It's an expensive process particularly with carburetors... with modern fuel injection you adjust the fuel map with a computer and changes are immediate rather than pulling the carbs, changing something, reinstalling them, checking the result ... and repeating many many times while paying a bunch of $$$ per hour for the dynamometer.
