The phone number is 678-3262. So, find people who know you well and think favorably of you to write your recommendations. Professors usually like to see a copy of your transcript and your personal statement. Ask professors what information you can give them that would be helpful in writing the reference. Do not bug them about getting the reference in on time.
Professors typically have a policy about whether they show the letters they write to students.
If seeing the letter is important to you, it is important to tell the professor when you request the reference. The professor can let you know his or her policy. Professors need plenty of notice about writing references. Because professors get requests from many students, each of whom is applying to multiple places, it is a good idea to ask professors to complete your reference on the Columbia College Graduate and Professional School Reference Form. This is available from 202 Hamilton Hall.