Extra input to express my interest in a major? Any help?

I am not too familiar with the common app as I just signed up for it but I want to express my interest in a major that I want to study by sharing some works, projects, and internships that I achieved in school relating to the subject. I am applying ED to this 1 school and apparently expressing interest in a certain major helps a lot in admissions. So I was wondering where do I put these in common app? please help me out thanks!