Quick Question on Common app

Hey Guys!

So I have been doing research with a professor at a state university as a high school student.
I will be applying to college this year and was wondering how do I show that I did research at a university.
Should I get a letter of recommendation from the professor? Or just list it in EC?
I REALLY want to highlight as I feel it will benefit my application as a whole.

Any advice would be appreciated!
Thanks!