Preparing a Finnish gap fire is fair easy to do if you have a supply of wood available. Pine is typically your best option to to get a quick, long lasting fire going, but Birch can also be used for this task as well.
The set up is basically two logs laid horizontally with one on top of the other and it is fairly easy to do, especially if you are good with a hand axe. These fires are great when you’re sleeping outdoors in a lean-to shelter or under the tree canopy in very cold or arctic conditions. They burn all night which let you stay warm and get the sleep you need for survival.
Just remember to carve a groove in to the lower log, and fill it up with the leftover whittlings, small sticks, and maybe the bark. Plus, the sticks between the logs, that make the air flow gap should be fresh and moist so they wont burn as fast as the logs. Check out the tutorial.