Hi Ahimsa,
Asana Pranayama Budhra Bandha (APMB) is ‘the bible’ for many yoga practitioners and teachers.
It is easy enough to be understood by newbies (most parts) and deep enough to bring deeper awareness to teachers.
I personally know the writer who was Swami Nishchalanda who was a personal disciple of Swami Satyananda.
You will hear much conflicting advice and opinions from yoga teachers on breathing. Especially between those influenced by the Ashtanga lineage compared to all the other spiritual lineages.
In general, with ‘genuine yoga practice’ the key to breathing (at least for beginners) is to relax.
Nice easy slow relaxed breathing.
Easiest way to do this is lying on the back at the start, in Shavasana (check index of APMB).
Good idea to rest one hand on abdomen, and other on chest.
And try to let go, but not trying too hard, and have some fun as you explore your breathing.
As you inhale, try to breathe into the abdominal area (at least it will feel as if the breath is going there) gently, and if possible allow the belly or abdomine to rise slightly.
And as you exhale, try to again let go, and allow the belly to sink back down.
Focus on this for a while, and then practice this each day for a few minutes.
Well worth doing this for a couple of weeks before moving on to the thorasic breath.
The breath is the ‘key’ to going inwards. Well worth taking your time to allow this abdominal breathing to become almost second nature, before rushing on to any other techniques in yoga.
I wish you well ahimsa.
Best Wishes,
Dave