Not sure why someone has suggested you don't need a shadowing role. Shadowing is perfect experience for applying to med degree as it gives you a direct insight into what being a doctor is like. Interviewers and admissions staff want to see that you have some awareness of the roles challenges of being a doctor.
A caring/ volunteering role can bolster your application too. Some students aren't able to obtain shadowing as it can be difficult to secure without connections, and a voluntary role with ill/ vulnerable people can be used in lieu.
CV- list your grades, work experience, jobs, roles of resposibility/ extra-curriculars and awards.
In your covering letter you you write a few short paragraphs. Introduce yourself briefly, what you can offer (why you make a good candidate) and what you hope to gain from the experience.