Mezuzah: (Lit. “doorpost”): A small parchment scroll upon which the Hebrew words of the Shema are handwritten by a scribe. Mezuzah scrolls are rolled up and affixed to the doorposts of Jewish homes, designating the home as Jewish. It also is reminding those who live there of their connection to G‑d and their heritage. The decorative Mezuzah Silver Brass Stone case containing the mezuzah scroll is just that: a mere container. What’s important is the scroll, upon which the first two sections of the Shema are handwritten. It begins with the eternal words “Hear o Israel, the L‑rd is our G‑d, the L‑rd is One.” . These selections both contain G‑d’s instruction to affix the mezuzah: “You shall write them on the doorposts of your house and on your gates.”
You should hang a mezuzah on just about every doorway that belongs to you. Notable exceptions are doors leading to bathrooms and small closets.
The mezuzah should be hung on the right side of the door, on the top third of the doorway. The mezuzah should be right-side up, and slanted so that the top of the mezuzah faces inwards towards the room.
Here is the blessing once you place the Mezuza on the entrance frame: