The Torah states (Devarim 6: 6, 8): And these words, which I command you this day, shall be upon your heart…And you shall bind them for a sign upon your hand, and they shall be for a reminder between your eyes.” These verses are the source in the Written Torah for fulfilling the commandment to put tefillin on the arm across from the heart and on the head atop the brain.
Your tefillin bag contains two black leather boxes, usually covered with protective plastic cases, with straps bound to them. These prepared boxes are called “batim”, as they serve as “houses” for the parchments placed inside them. One is designed for the tefillin placed on the arm, the second for the tefillin placed upon the head.
The manner distinguishing between the different batim: The box designated for the arm is made as one hollow unit, whereas the box designated for the head is divided into four cells, one alongside the other. On the outer right side of the head tefillin, there appears prominently a letter ‘Shin‘ with three heads, and on the left side, a ‘Shin‘ with four heads.
The tefillin for the arm is placed on the weaker side, i.e., a person who writes with his right hand places the tefillin on his left arm, while those left-handed place it upon their right arm.
The person first must roll up his sleeve above the bicep on the arm’s upper portion, revealing the area where the tefillin are to be placed. Loosen the loop created by the knot in the tefillin strap, remove the hand tefillin from its protective plastic case, and place it on the upper portion of the arm muscle, slightly beneath the midpoint between the shoulder and the elbow, directly across from the heart (see drawing).
Then say the blessing: “Baruch Ata Adona-i, Melech HaOlam, asher kidshanu b’mitzvosav v’tzivanu l’hani’ach tefillin” [Blessed are You, O G-d, King of the Universe, Who has sanctified us with His commandments and has commanded us to put on tefillin].
From the moment the bracha is said until the tefillin have been placed on both the arm and the head, it is forbidden to speak or even gesture. Concentrate upon the connection between the mind, the heart, one’s actions – and Alm-ghty G-d.
Fasten the strap around the arm. Make certain that the knot is securely against the box, Continue winding twice more upon the base of the strap, around the muscle, then seven times around the arm between the elbow and the hand, and once around the palm. Leave the rest of the strap free for the moment (see drawing).
Now, take the head tefillin, remove it from its protective plastic box, and place it where the forehead ends, directly between your eyes. Place the knot shaped like the letter ‘Dalet‘ behind your head on the upper part of the neck (see drawing).
In the event that you make an interruption by speaking between the blessing and putting on the head tefillin, you make an additional blessing as you put on the head tefillin, “Baruch Ata Adona-i, Melech HaOlam, asher kidshanu b’mitzvosav v’tzivanu al mitzvas tefillin” [Blessed are You, O G-d, King of the Universe, Who has sanctified us with His commandments and has commanded regarding the commandment of tefillin].
The strap on the hand tefillin held in your palm is then wound three times around the middle finger – first around the base of the finger, a second time above the joint, and a third time again at the base. The remaining portion of the strap is wound around the palm, with the end tucked under the strap on the palm to keep it from coming loose (see drawing).
Illustrations provided by the Chabad.Org website