Help me understand these formula

combined_df[‘cases_per_million’] = combined_df[‘total_cases’] * 1e6 / combined_df[‘population’]

combined_df[‘tests_per_million’] = combined_df[‘total_tests’] * 1e6 / combined_df[‘population’]

combined_df[‘deaths_per_million’] = combined_df[‘total_deaths’] * 1e6 / combined_df[‘population’]