Letter of motivation for a Masters Degree

Hello,
I am a fresh member of this forum and I have a really hard time to express myself in English. Please forgive me for any spelling (or other) mistakes!
I have to write a letter of motivation in order to be considered for a masters programme in Sustainability and Corporate social responsibility.
Could you please help me to write it? Do you a have a sample letter to see what am I supposed to write?
Also, I haven't decided yet to which University I want to apply.
I am thinking of the Queen's university in Belfast, Leeds University, and University of Newcastle. If you have any suggestions about a University, please let me know.

Thank you very much in advance!