The Mezuzah itself is a parchment containing passages from the Torah known as the Shema Yisrael (Hear, O Israel: The Lord is our Lord, the Lord is One). These words summarize the commandment to the Jew to imbue the world with the oneness of God.
We place it on our doorposts so that His oneness may surround and protect us. The parchment must be written on leather by a skilled scribe, using a special quill and ink. It is important to purchase from reliable sources, as the market is full of printed or poorly written mezuzot.
The parchment is usually placed inside a protective covering. It is placed on all doors of the house, except bathrooms and spaces smaller than 2 meters by 2 meters, including hallways and dressing rooms.
On the right side, as viewed from the person entering the room where the mezuzah is placed. If it is the door of a house, it is placed to the right of the person entering, even if the door opens outwards. When there is no door (such as in a hallway), the importance of the rooms is considered, placing the mezuzah to the right of the person entering from the least important room to the most important room.
First, the appropriate blessing is recited, and then the mezuzah is affixed to the lower part of the upper third of the door, tilted from the outside in. It is customary to touch the mezuzah when passing through the opening where it is affixed.