At first, but once you reach nostril nirvana you unlock the ability to breathe with your third nostril

Can I consider my mouth my third nostril and reach nostril nirvana already?

There's a joke in Russian quite popular among small kids: "The hedgehog learned to breathe through his butthole. One day he sat down to rest and suffocated".

(Hedgehog is the hero if many slightly absurdist jokes).

Hedgehogs can't (to my knowledge), but turtles can! A fact that seeks any opportunity to be shared. (Example source: https://www.livescience.com/61018-turtles-breathe-through-bu...)

You were always there :)

Only waiting to realize.

Let me actually encourage you try this. Imagine you have a third nostril placed between the 2 real (forming a line or a triangle - whatever you like better), visualize and "sensualize" (do your best imagining it in details and feeling it) breathing through 3 nostrils. As a result this may trigger a nasal congestion relief. Try this the next time you catch a cold.

Not going to lie: "Naturally we breath out of one nostril at a time" had me looking very confused! I even tried contorting my face to get one of my nostrils to close, haha

If you pay attention, one of the nostrils are likely to be more active (as measured in air flow) at a given time and the active nostril will switch side from time to time, perhaps something like every couple of hours.

I think that just depends on which nostril is the least clogged at that particular time.

It mainly depends on which turbinates are more blood filled at a given time. See e.g. https://en.wikipedia.org/wiki/Nasal_cycle

There’s an advanced variant in which you don’t use the fingers and attempt to manipulate the breath using the lungs only—its called anulom vilom

That can't be right, nostrils "merge" at the back of our throat?