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.
It’s always a smart idea to offer to write a letter of recommendation for a colleague who you know is well qualified for the job in question. Consider it good career karma; after all, you never know when you’ll need a letter of recommendation for yourself, and your colleague may be happy to return the favor.