The Torah specifies "corners" (kanfot) — four-cornered garments. Three corners: exempt. Five corners: obligated (four corners is the minimum trigger).
Question 2
Are women obligated in tzitzit?
Tzitzit is a positive, time-bound commandment (worn only during the day). Women are exempt from such commandments, though they may voluntarily wear them.
Question 3
You borrow a friend's tallit for a few days. Must you attach tzitzit?
A borrowed garment is exempt from tzitzit for the first 30 days. After 30 days of continuous borrowing, you must attach tzitzit.
Question 4
Are cotton garments obligated in tzitzit?
The Torah specifically mentions wool and linen. Other materials: the Rambam holds they're rabbinically obligated — not Torah-level, but still required.
Question 5
Can you wear a tzitzit garment at night?
Tzitzit is a daytime obligation. Night garments are exempt. You can wear them at night, but there's no mitzvah in doing so.