You accomplish two important things in presenting research experience as part of your application portfolio. A research project, whether in the sciences or another discipline, speaks to your in-depth mastery of a subject as well as your ability to see a long-term project through to completion.
Start planning research experiences early. Your professors have ongoing scholarly projects of their own and regularly take on students in independent study projects. These projects can mature into a senior thesis. Talk to your professors about getting involved in an independent study or other research project.
There are also many discipline-specific and health-related off campus internship and fellowship opportunities, which you can find listed on the MHC Fellowship page. The College may provide funding to support student summer research and internships.