The Mezuza By Elisabeth Syré
Origin:
A literal fulfillment of Deuteronomy 6:9 (see below)
It is not a magic talisman. It is a symbol of willingness of the inhabitants of the home on which it is placed, to obey the Bible and to show respect for the Word of God.

Usage:
Applied to the doorpost of the home by nails, screws, glue or any other means. It is placed on the right door- post as you enter the home on the main entrance door. It is placed about head height, slanted slightly in, towards the inside of the home.
Some people place them on every door - inside and outside.

Description:
What is often called a mezuza is actually a mezuza cover. The real mezuza is the scripture itself which is inside the cover rolled up like a scroll.
The mezuza cover is meaningless without the Scripture verses inside. The verses are Deuteronomy 6:4-9
Traditional Jews believe these verses have to be done by hand in calligraphy by a rabbi in Hebrew in order to have our God is the proper blessing.
These handmade scrolls are very expensive and cost up to $100, done in the proper way as it takes many hours to do this with a magnifying glass.
This is the meaning of the Hebrew scroll:

Deuteronomy. 6:4-9
4. Hear, o Israel, the Lord our G-d is one Lord.
5. And thou shalt love the Lord thy G-d with all thine heart, and with all thy soul, and with all thy might.
6. And these words, which I command thee this day, shall be in thine heart.
7. And thou shalt teach them diligently to thy children, and shalt talk of them when thou sittest in thine house, and when thou walkest by the way, and when thou liest down, and when thou risest up.
8. And thou shalt bind them for a sign upon thine hand, and they shall be as frontlets between thine eyes.
9. And thou shalt write them upon the posts of thy house, and on thy gates.