The commandment to attach fringes to the corners of garments, "tzitzit", is written in the Torah. Its purpose is that which the Torah itself tells us: "You shall see it and remember the mitzvot that the Lord has given you".
Therefore, according to the Masters of the Mishnah, the tallit should only be worn in the morning and, precisely because it is written "You shall see it", the tallit should be worn every day.
There are two types of tallit: one is smaller, "tallit katan", and is worn all day under one's clothing; the other is larger and is worn only during morning tefillot.