Motivation letter for internship

Hi everyone,

I am about to apply for Butterfly Consulting LLC that is seeking for part-time interns for six months. The selected interns will be responsible for assisting in business development through helping identify and develop business opportunities for the company.
I have never write a motivation letter before and I would like to ask if someone from you knows how to write it for the application above. English is my second language and I have difficulties on writing skills.

Thanks in advance,
Arta