When you participate in an experience (work/activities) more than once, you can enter "yes" in the checkbox next to the "repeated" field.
For instance, if you worked as a paid EMT each summer for 3 summers, you can list paid/employment "EMT" since the EMT work was repeated (each summer, for 3 summers). You can add additional date ranges for this work. In other words, you can list EMT once and then describe the work experience, as well as your work hours (e.g., 500+ or number of weeks per summer and average number of hours per week) in the space provided on AMCAS.