• Talked about my qualifications – what I had studied, what I was currently studying and my general level of achievement including notable assessment in which I performed well.
• Talked about my work experience – paid and unpaid, and what skills I learned during my time as a working professional (admin, business acumen, IT skills) and why they would benefit the UN.
• I then went into specific details of my strengths and skills – i.e research, communication, team work and so forth.
• I talked briefly about my language skills (english, obviously, then some knowledge of french and spanish though I admitted it was limited).
• I talked about why I was applying and what aspects of the UN work particularly interested me.

How I did it isn’t necessarily what is a ‘winning’ cover letter, but should give you ideas on how one writes a cover letter.