Every rule in popular Vastu comes back to a few ideas, and this section sets them out one at a time before any room or door is discussed. If you read nothing else here, read the first two guides, because the later ones keep referring to them.
The first idea is direction. The classical tradition gives each of the eight directions a guardian deity: Indra in the east, Agni in the south-east, Yama in the south, Nirriti in the south-west, Varuna in the west, Vayu in the north-west, Kubera or Soma in the north and Ishana in the north-east. The elements and planets that later practice attaches to the directions are real traditions, but they come in more than one version, and not all of them are in the building texts. The guide on the eight directions separates the layers by age.
The second idea is the Vastu Purusha Mandala, a square grid laid over a plot, most often eight by eight or nine by nine, in which each square belongs to a deity. The 81 square version has 45 devatas, 32 on the outer ring and 13 inside, with Brahma at the centre. It is a planning device, not a map of good and bad rooms, and seeing it that way takes a good deal of the fear out of the subject.
The third piece is the relationship between Vastu and astrology. People often ask whether a home should be matched to a birth chart. The guide here says what can responsibly be said: that the 4th house is read for the home in Jyotish, and that this is a separate matter from the direction of a door.
Throughout, the labels are the same. A statement is classical if we found it in a verse of a named text, modern if it is a recent convention, and disputed if the sources or translators disagree. The method page explains how these are applied.
When you are ready to move from ideas to a real home, go on to the rooms, where the entrance and its 32 padas come first, or to homes, which covers flats and plots.