What is a mezuzah?
"And you shall write them (the words of the Shema) on the doorposts of your house and on your gates." A mezuzah is usually thought of as an ornate, gilded object that is affixed to a doorway. Technically, it is the little parchment inside of the container that is the actual mezuzah. To some it provides spiritual and physical protection, fortification, and reinforcement to the home and the souls of all who dwell therein.

What is the purpose of a mezuzah?
The mezuzah is a constant reminder that our homes and everything therein belong to God, and must therefore be used properly. The mezuzah also serves as protection for the entire home. On every mezuzah is inscribed God's name, "Shadai," which is an acronym for "Shomer Daltot Yisroel," the Guardian of the doors of Israel

How do I put up a mezuzah?
In some homes or apartments, mezuzot are affixed on every doorway with the exception of the bathrooms. The mezuzah is affixed on the bottom of the upper third of the right doorpost (looking in) and should be at an angle so that the top of the mezuzah is pointing to the inside of the house or room.

Why is the mezuzah attached to the right doorpost?
The Talmud derives from a verse that the mezuzah must be placed on the side which you encounter first when you enter. The average person steps first with the right foot and then the left foot. According to Kabbalah, the right side represents kindness and the left side is symbolic of divine severity. Therefore the mezuzah, which is intended to bring God’s blessings and protection upon the house, is placed on the right doorpost.

What is inside the mezuzah?
The mezuzah contains a scroll of parchment containing two passages from the Torah --the Shema and Vehayah . These portions can be found in prayerbooks, as these sections are part of the daily morning and evening prayers.

Do mezuzahs need to be checked?
For a mezuzah to be kosher, all the letters in the scroll must be complete. Due to humidity and other factors, letters can fade or crack, rendering un-kosher an originally beautiful mezuzah. Periodically, you should take the scroll out and have it inspected by a scribe to ensure it is still kosher.