This practice is the ocean breath otherwise known as the ujjayi breath and it is one of the more common forms of breath work or pranayama in the yoga tradition.
It involves breathing in through the nose and then exhaling with the mouth closed with a constriction at the back of the throat like you're fogging up a mirror.
So you can try that out by pretending you're trying to fog up a mirror with your breath with your mouth open and then close your mouth and keep that exhale going and has a nice sound kind of like a wave coming into the shore hence one of the names that's called the ocean breath.
So let's practice together inhaling through the nose and then exhaling closed mouth with that constriction at the back of the throat inhaling through the nose and exhaling through the nose with that constriction at the back of the throat inhaling through the nose exhaling through the nose with that fogging up the breath constriction at the back breathing in through the nose exhaling breathing in through the nose exhaling through the nose closed mouth When I'm using this practice to try to fall back to sleep which it really helps me with I also like to bring in the image of a wave the water going back out to sea and then crashing into the shore so I invite you to bring that imagery in as you inhale the water rushing back out to sea and then as you exhale the wave crashing to the shore if that helps to deepen your practice so you can give that a shot if you'd like to keeping that going and keeping in mind this works as any extended exhale practice does it helps to parasympathetic rest and relax energy and tone back to your nervous system working with that vagus nerve to help to bring balance to a stressed out nervous system as you continue breathing in through the nose and then exhaling with that constriction at the back of the throat and there you have it the ujjayi breath ocean breath extended exhale breathing breath work or pranayama that will help to bring calm to an activated nervous system