Thank you for spelling out where it lost you. 0.1.7 rewrites the How To around your questions.
It says what a road, a face and a heading are, and gives the gas rule as numbers: a Top or Main face needs 0.26 air, a Deep face 0.63, and faces in a row their sum. Point at a face, or tap it with the Face tool, to read its air. A withdrawn face restarts by itself once its air is clean; Furnace Up is the quickest fix.
Doors, cloth and overcasts come down free with the same tool; roads and faces don't. The surface can't be cut, so a shaft dug upward takes in no air, and the game now says so. The shop's Second Downcast gives a second current.
Cloth on the face at a dead end splits it in two: air runs in one side and out the other.