College admissions officers assess applications holistically, meaning they evaluate the “whole” student. No factor (including grades, test scores, or extracurriculars) is considered in a vacuum; rather, these pieces are all assessed in the context of each student’s unique background.
With that being said, a student’s academic record (including their grades and course selections) tend to be the most important part of each application. College vary in terms of which factors they consider and how they weigh them; most colleges provide insight into these factors on their Common Data Set document (try searching the web for “[College Name] + Common Data Set”).