One of the six question types on the MCAT Verbal Reasoning section is the Main Idea question. These questions ask for a restatement of the author's main point, the primary idea, or the overall gist of the passage.
A key strategy for Main Idea questions is to read the answer choices and pay attention to their scope. Wrong answer choices will generally be too broad or too narrow. Eliminate those quickly and look for the answer choice that best matches the scope of the main theme.
Main idea questions are common in this section. So it's a good idea to look for the main idea while you initially read the passage. Key words to look for include "theme," "idea," and "purpose."
Try taking a practice exam from Kaplan. They have wonderful resources and guides as well. Online MCAT Prep with KAPLAN