Putting together a "quick note"

Earlier today I had an informational interview with an analyst at a top MM for ER, and long story short he told me that he liked my past experience/what I had told him and said that if I send him my resume and a quick note on a company of my choice he could make things happen for the summer.

So what exactly should I include in a quick note? I've written bits and pieces of actual notes over the summer, but never one completely on my own. I was going to pick a small cap name, but otherwise would appreciate some guidance on how to go about writing it.

Thanks brahs