An Ancient Tradition
On the back of the scroll, a name for G-d is written. The scroll is then rolled up and placed in the case so that the first letter of the Name (the letter Shin) is visible (or, more commonly, the letter Shin is on the outside of the case). The scroll should be handwritten by a sofer (someone trained in writing ritual text). A small ceremony called Channukat Ha-Bayit (dedication of the house) is performed.
Why the Mezuzah Is Affixed at an Angle
The rabbis could not decide whether it should be placed horizontally or vertically, so they compromised. It reminds us to keep a good balance in our lives. A mezuzah should be affixed on outside doors and on any doors you walk thru to enter a living space. They are not placed on the doorposts of bathrooms. When you pass through a door with a mezuzah on it, you can kiss your fingers and touch them to the mezuzah, expressing love and respect for God and reminding yourself of the commandments contained within them.