Shifting can be smooth or it can be creaking annoying and might even break a chain.
The secret to smooth shifting is timing the shift to a point when there is minimal tension on the chain.
On the other hand, we have to be pedaling while shifting, and pedaling creates tension on the chain - so what is the solution?

Combining the surge, soft pedal, and shift together!

With the surge, we're creating a very quick acceleration.
With the soft pedal, we are taking advantage of that quick acceleration - using the momentum we gained to keep pedaling, just softer - without actually pushing hard on the pedals. This move enables us to spin the pedals and still have very low tension on the chain.
The next move will be to click that shifter, and experience a nice and smooth shift!