The Vastu Purusha Mandala forms the basis on which you can make a grid of your house.
The Vastu Purusha Mandala helps you to devide the house in the eight directions and make a grid of where to place which room. The mandala is based on the Vastu Purushu deity who lies in the mandala with his head to the north east and his navel the center and his lower body lies in the south west.
Desiging your house based on the Vastu Purusha mandale can be difficult, because most of the times your house is already designed and you can not easily change the purposes of the rooms of your house.
If you can make some adjustments make sure your house is a square or retangle and has no cut corners. It that way your house is balanced and you can put the Purusha Mandala like a template on your house. Most ideal is that the outer walls of your house match the north, south, west and east directions. Lots of time you can't change that, just keep it in mind if you move one day and try to adjust your house according to Vastu as much as possible. Accept the things you can not influence and adjust what you can.
For ideal positioning you have to make two grids if you have a garden and one if you haven't and live for example in an apartment.
You make one parusha mandala for your plot (paramasavika) and one grid for the house plan itself.
A common Vastu Purusha grid is a square divided in 9x9 equal squares, creating a grid with in total 91 squares (called a paramasayika). In the Vastu Purusha 45 different deities house in 45 regions of the grid. The center of the grid of your plot is called Brahmanabhi. The center of the grid of your house is called Grihanabhi.
You can use to Vastu Purusha grid to lay it as a template over the drawings of your plot / house. Making sure the middle of the north side of the grid matches the north of your house. Based on the created template you can start moving objects and or change purposes of the rooms.
Try to keep the center of the grid / your house wich Vastu calls the Brahmastana as empty as possible. According to Vastu knowledge disturbing the center of a house leads to misunderstandings between family members.