how to build a fire from scratch ?
you have nothing but your hunting gear, coat and rifle and you got lost. you have no matches, lighter, no pre packed anything, what to do ? and its getting dark and cold.
(i have no idea, just asking)
Firstly, being in a situation where it is possible to succumb because of a lack of a fire, without an adequate means to build a fire is an egregious and unforgivable mistake!!
Secondly. the means by which (yes you should have more than one) you choose to make your fire will depend upon your proven abilities to make a fire by the selected methods and your preferences.
In the situation you describe above I assume a knife is part of your hunting gear and you have nylon or leather boot laces. If you have those two items and daylight I would opt for constructing and using a bow drill set. I firmly believe that every woodsman should develop the ability to build such a set and should become thoroughly familiar with using it to light a fire with confidence. With good quality materials I can get an ember in approx. 1 minute. If you lack shoelaces, paracord etc you can use natural cordage however this takes some real pracitce before hand and is considerably more applicable to a strap drill rather than a bow drill set. If you lack a knife to carve your bow drill set you had better be in an area with knappable geology and better be somewhat skilled at knapping.
If there is no way you can build a fire remember the concept of radiant loss of heat from black (warm) bodies that is found in physics. In its most simplistic form for our purposes that can be stated in this fashion--- a warm object under a cold open dark night sky loses heat at a faster rate than if the object was covered. Hence, if I could not build a fire for some reason (highly unlikely if you ALWAYS carry at least 3 means by which to build a fire) I would quickly begin building a thick debris shelter.
Incidentally I always carry at least 3 means by which to build a fire. Some of my favorites are Zippo( filled), Mischmetal/Ferro rod, magnifier, waxed strike anywhere matches in waterproof case, knife with wide flat spine (tempered high carbon steel only) to use as striker for a Mischmetal/Ferro rod or as a striker for flint,quartzite etc geology present in the area and to carve a bow or strap friction fire set.
Remember, do not go afield without a means by which you can build a fire.