To experienced zazen practitioners: how does one focus on the breath exactly?

Context: I've started zazen practice after reading Three Pillars of Zen. My plan has been to start with counting the breath, then following the breath, then finally to move on to shikan-taza.

At this point in time counting the breath goes very well, I don't lose count or focus. I also tried shikan-taza but, predictably, found it too hard for now. So now I'm trying to follow the breath.

The question is, what do I pay attention to, exactly?

There are so many things going on with the breath: the sensation of air against the nostrils and passing through the nose and larynx, the expansion of the chest, the movement of the diaphragm, etc etc.

The book, as well as various online sources I consulted, talk about hara or tanden, a point some two inches below the navel and three inches inwards. Well... there's nothing really there. I can concentrate on any place on my skin or in my muscles, e.g. feel the air against my nostrils, because such places have lots of nerves in them; but how the hell do you concentrate on the tanden, assuming it even corresponds to anything real? I'm wondering if one dude a few thousand years ago made it up, as part of the chakra system, and everyone else has been deceiving themselves there's something to focus on there through self-suggestion and not wanting to contradict their teacher.

Secondly, even if I put my mind in that area (without getting back much in the way of sensations to focus on, because again, there's nothing there), what does that have to do with focusing on the breath? It's not like the lungs go down all the way to the lower stomach. Isn't that focusing on two things at once, 1. the current inhalation or exhalation and 2. the lower abdomen? Kinda defeats the purpose of achieving "one-pointedness" of the mind...

I'm interested in specific, practical, jargon-free answers, please.

EDIT:

I suspect a possible reply might be "well, if tanden doesn't work for you and nostrils do, just focus on that". If this is you, but you personally still find the method involving the tanden practicable, I'd still like to understand that.

Submitted February 10, 2019 at 04:51PM by markusramikin http://bit.ly/2SAWDD9