At the hairline, centered between the eyes, within the zone from ear to ear. Not too high, not too low — precisely at where the hair begins.
Question 2
A left-handed person — on which arm do they wear the arm tefillin?
The principle is "your weaker hand." For a lefty, the right arm is weaker — that's where the tefillin goes. Always the non-dominant arm.
Question 3
Why aren't tefillin worn on Shabbat?
Tefillin are called an "ot" (sign). Shabbat and Yom Tov are also called "signs." Wearing a sign while being a sign is redundant — so tefillin are not worn.
Question 4
Which tefillin is put on first?
Arm first, head second. The Torah mentions "hand" before "between your eyes." Remove in reverse: head first, arm second.
Question 5
How many blessings are said when putting on tefillin?
Two blessings: one for each. "L'haniach" for the arm (the act of placing), "al mitzvat" for the head (the commandment of tefillin). Don't speak between them.