References are one-to two-page letters provided by former teachers, lecturers and professional colleagues as part of the university admission process. They are used to highlight the student’s academic history and character that is used so universities are able to have a better insight of the student applying. These can be written by academics and professionals who have worked with you or know you personally such as managers, current or former colleagues, career advisers, advisers and so on. References cannot be written by yourself or include family members, friends or partners. Often universities will ask for letters of recommendation that are signed, headed and dated in the reference and are most likely not to accept references that come from non-professional email accounts such as Hotmail, Gmail, Yahoo, etc. Most universities will ask for one to two references, while some universities like the University of Cambridge as well as other top world universities will ask for as many as of three. When starting the application process, you can contact someone asking them if they would be happy to provide you with a reference. Supplying the person with supporting information about you such as through a brief summary, transcripts, CV etc. will help the referee provide relevant information as part of your application. 
Here is a sample of a reference request:
Dear _____, I hope you are well. I am currently applying for ______ and was hoping you could provide a reference for me. As my current/former ______ and with your permission, I believe you could improve my chances of obtaining an offer from ______ I have attached my relevant documents for your reference. Please let me know if you need any other information from me.  Thank you in advance for your assistance.  Sincerely,  _______