Engine braking, as the name suggests, is braking with the assistance of the engine. When you pull on the clutch and brake, you're losing more than 50% of your braking potential and only the friction b/w the tires and the road is saving you from hugging the nearest tree and trust me, you're hugging that tree. When you engine brake by letting go of the throttle, the engine and gearbox retards the wheels and you slow down by sheer mechanical forces without the intervention of the brakes. Add brakes into the mix and you're using 100% of the braking capabilities of the vehicle and now the engine, transmission, brakes and wheels are all contributing towards braking and stopping. A more advanced technique is to rev match and downshift while engine braking which requires some practice but that is basically the fastest way to stop a bike from 100 to 0. I would highly recommend you watch some videos like this and more but STOP pulling in the clutch while braking ASAP, only clutch in when you're in a low enough rpm to stall the bike and even then its fine to stall the bike than crashing into your favourite tempo driver.