Edit Page sidebar custom options

On the WP site I’m learning, when you go to the dashboard and edit a page, there are several sections in the right sidebar that look like they were custom-built.

For instance, under the usual ‘Publish’ and ‘Page Attributes’ boxes on the right sidebar, there is an ‘Events’ box with custom checkboxes that pertain to the type of event relative to the company.

How does one create these custom options? Where should I look to edit them? I looked in functions.php, but couldn’t find anything related. The ‘Admin Menu Editor’ plugin is installed, but it only looks like you can change the left nav in the dashboard.