You are required to have three letters of recommendation submitted on your behalf. The letters should be submitted by instructors in a discipline related to your proposed field of study who are in a position to analyze your abilities and academic promise. Letters may be submitted online or on paper via regular mail; online submissions are strongly preferred.
You put your own reputation on the line when you write a letter of recommendation. If you feel you do not know the person well enough, or they are somebody you cannot in good conscience recommend, decline their request.