The Mitzvot of Wearing Tefillin
“And you shall bind them for a sign upon your arm, and they shall be for frontlets between your eyes” (Deuteronomy 6:8). וּקְשַׁרְתָּם לְאוֹת, עַל יָדֶךָ; וְהָיוּ לְטוטָפת, בֵּין עֵינֶיךָ

In this verse, the Torah commands us to put on tefillin on the head and arm. The Rambam in his Sefer HaMitzvot points out (positive Commandments 12, 13) that this commandment is repeated in the Torah four times.
The donning of tefillin is an essential observance for Jewish males above the age of bar-mitzvah. According to the prophet Isaiah (38:16), All who don tefillin are granted a longer life, as is written, ‘O L-rd, with these things men live’.

The parts of the tefillin
How the tefillin are wrapped
The batim (boxes)
Cowhide (gassot)
Sheepskin (dakkot)
The tefillin straps (retzu’ot)
The torah passages (parshiot)
The parchment
Inserting the Torah passages
The form of the letters
Tefillin of Rashi and Rabbeinu Tam
How to care for your tefillin