Internship Letter of Recomendation

<p>This past summer, I interned at a hedgefund in NYC. When i approached a partner for a letter of recomendation to college, he told me to write on and that he'll sign it. Im kinda panicking bc I dont know how to do this! Should I say im the greatest thing since sliced bread? Does anybody have any templates of ideas i can use?
PLEASEE</p>