Learn Hardcore Portuguese (Portugal): Com paciência, a massa fica mais leve. - With patience, the dough becomes lighter.

Putting a comma after com paciência marks it as an introductory adverbial phrase (‘with patience’). It emphasises that patience is the condition for the dough to turn out lighter. The comma is optional, though. You could also say:
A massa fica mais leve com paciência.

What does massa mean here?

In this context, massa means ‘dough’ (the mixture you knead to bake bread, cakes, etc.), not ‘mass’ or ‘crowd.’

Why is there a definite article a before massa? Could we drop it?

Portuguese often uses the definite article before a generic noun: a massa = ‘the dough’ (in general or in this recipe). Dropping it (saying just “massa fica mais leve”) sounds less natural in European Portuguese.

What is the function of the verb ficar here?

Ficar can mean ‘to become’ or ‘to end up.’ In “a massa fica mais leve,” it shows a change of state: the dough becomes lighter.

Could we use estar instead of ficar?

You could use estar (“a massa está mais leve”), but ficar emphasises the process or result of becoming lighter, whereas estar simply describes its state at a given moment.

Why do we say mais leve without adding do que?

The comparison is implicit: lighter than before (or lighter than a dough made without patience). In Portuguese you can leave out “do que” when the second term of the comparison is clear from context.

Could we say fica leve instead of fica mais leve?

Yes, but fica leve just states that the dough turns out light. Fica mais leve emphasises that it gets lighter (e.g. compared to a denser version made without patience).

Can we move com paciência to the end of the sentence?

Absolutely. Word order is flexible:
A massa fica mais leve com paciência.
Putting it at the start (with a comma) gives it more emphasis; at the end it’s more neutral.

How do you pronounce paciência in European Portuguese?

In IPA it’s approximately /pɐ.si.ˈẽ.sjɐ/.
A rough English guide: “pah-see-EN-syah,” with the stress on the “EN” syllable and a soft “n” nasalised before “s.”