By the last chapter, the terms you have stacked up are a working fluid simulator.
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Play with the finished lab first, then learn the terms one by one and come back to it.
You can follow a particle or watch one point. The difference between the two views is the advection term.
What flows in must flow out. The divergence is the balance of that ledger.
Pressure is the force that removes divergence. Bernoulli is a special case of what it does.