What can i say to a college admissions rep ?

My counselor said to email a college admissions rep and to "make a bridge" to the school I wanted to go to.

I don’t know what this means ! I only just graduated highschool and I didn’t even do well at that.
I’m taking the classes I need to take to transfer and I want to be a Dermatologist which means I’m trying to get into Pre-Med.

Any ideas ? Has anyone ever emailed a rep before ?? HELP !!