Learn Hardcore Italian: Se le onde saranno più alte, il bagnino ci farà uscire dall’acqua. - If the waves are higher, the lifeguard will make us get out of the water.

se + present, future (the everyday style):
Se le onde sono più alte, il bagnino ci farà uscire dall’acqua.
se + future, future (more formal or to stress futurity):
Se le onde saranno più alte, il bagnino ci farà uscire dall’acqua.
Both are correct; the second simply highlights that both the condition and its consequence lie in the future.

What is the function of ci in ci farà uscire dall’acqua?

Here ci is a clitic pronoun standing for “us.” In the causative construction fare + infinitive, the person who is made to do something is a direct object. So:
il bagnino → subject
ci → direct object (“us”)
farà uscire → “will make (us) exit”
together: the lifeguard will make us get out of the water.

How does the fare + infinitive structure work in this sentence?

This is the Italian causative. You conjugate fare in the needed tense (here futuro semplice: farà) and follow it with another verb’s infinitive (here uscire). The meaning is “cause/let/make someone do something.”
Example breakdown:
il bagnino farà uscire → the lifeguard will have someone exit
ci farà uscire → …will have us exit

Why do we say uscire dall’acqua instead of just uscire l’acqua or uscire acqua?

Uscire is intransitive and needs a preposition to indicate “from.” You use da + the definite article:
da + l’(acqua) → dall’acqua
so uscire dall’acqua literally means “to exit from the water.”

What’s the difference between using se and quando here (e.g. Quando le onde saranno più alte…)?

se = “if,” indicates an uncertain or possible condition.
quando = “when,” signals something the speaker expects to happen for sure.
If you’re certain the waves will rise at some point, quando is fine; but se leaves it open whether they’ll actually get higher.

Can we invert the order of the clauses and still be correct?

Yes. Italian word order is flexible. You can say:
Il bagnino ci farà uscire dall’acqua se le onde saranno più alte.
The meaning stays identical; you’re just placing the main clause first.

Why is there no di in più alte? Don’t comparatives need più… di?

When you specify the second element of comparison you use più [aggettivo] di (e.g. più alte di ieri = “higher than yesterday”). Here, più alte stands alone to mean “higher” in a general sense, without naming what it’s higher than.

What type of conditional is this called in Italian grammar?

It’s a periodo ipotetico di primo tipo (first conditional). Normally you see se + present, future, but you can also use se + future, future for a more formal register or to emphasize futurity.

Why are we using le onde (plural) and can we refer to a single wave?

Onda is a feminine noun. At the beach people normally talk about le onde (the waves) in general. If you wanted to speak of one big wave you could say:
Se l’onda sarà più alta…
but usually you expect multiple waves rising.