I'm not sure anyone here can provide you with an answer that you could comprehend or institute. If you are able, you would do best finding a qualified meditation instructor and handling this in person, rather than in a disjointed rambling over the Internet. There seems to be too much misunderstanding here to be able to clear up using this medium. Also, too many cooks spoil the broth, and such (if you understand what I'm hinting at, as a source for your confusion).
Mark R.:
I am confused to a high degree about what to do.
I'm trying to concentrate to the nostrils airflow as of now, sitting (i can keep my body still enough). I don't know what to do with unpleasant feelings that arise.
Unpleasant feelings, then, for you become a hindrance. You have to get beyond this hindrance first before your meditation will yield the benefits you seek.
If you're planning on using meditation to help you get beyond this hindrance, then you're going to need to develop the ability to concentrate upon and contemplate the nature of the hindrance so that you can see it for what it is and let go of it. But this needs to be accomplished first before you will be able to reliably carry on with making further progress with developing
samatha (calming and concentration of the mind) and
vipassana (insight contemplation on phenomena and the Dhamma).
Mark R.:
In MCTB i'ts written that first one should begin to practice concentration on an object at least to access concentration. It is also said that the mind faculties (my term) of insight and concentration are different and can be developed independently or in combination.
That is true – i.e. insight and concentration are different – and yes, they can be developed independently or in combination.
Mark R.:
From this i understand that developing concentration helps the practice of insight. If i suppose that it would be great to attain access concentration first, why should i begin with something dispersive as walking meditation, that it looks like more an insight practice (from Daniel's post "paying a lot of attention to every little movement...")?
Because walking meditation serves to redirect the mind away from the original hindrance and to focus it on another activity and phenomenon. Sometimes that works, sometimes it doesn't. It can become kind of tricky, trying to follow all of these suggestions, can't it. That's why I suggest that you find someone qualified who you can discuss these things with in person rather than using the Internet.
Mark R.:
Another way to reformulate most of the questions asked before, is: if one can often change object or method and still proceed on what he has established to attain, or if it's best to stick with one thing despite the conditions or the mind whining. Thanks.
You'll need to clear up the "mind['s] whining" first before you'll be able to reasonably make any progress on the fronts of calm and insight into the Dhamma. This is why, in the suttas, Gotama stresses the importance of letting go of worldly concerns when in the process of meditation, as in this passage from the
Anapanasati Sutta (MN 118):
"Bhikkhus, on whatever occasion a bhikkhu, breathing in long, understands: 'I breathe in long,' or breathing out long, understands: 'I breathe out long'; breathing in short, understands: 'I breathe in short,' or breathing out short, understands: 'I breathe out short'; trains thus: 'I shall breathe in experiencing the whole body'; trains thus: 'I shall breathe out experiencing the whole body'; trains thus: 'I shall breathe in tranquillising the bodily formation'; trains thus: 'I shall breathe out tranquillising the bodily formation' — on that occasion a bhikkhu abides contemplating the body as a body,
ardent, fully aware, and mindful, having put away covetousness and grief for the world. I say that this is a certain body among the bodies, namely in-breathing and out-breathing. That is why on that occasion a bhikkhu abides contemplating the body as a body,
ardent, fully aware, and mindful, having put away covetousness and grief for the world."