The General menu allows you to edit all data that can be used in multiple places in the site. This global content is not tied to a specific page or function. These data settings are also called the "globals".
What data is editable here is entirely determined by the website developer. Examples of such data are address information, social media links, opening hours, information in the footer etc.
Globals can also be used for general functional settings such as counters, mappings and specially tailored created functionality. They can be split between categories in the gray menu and can also be language and site specific.
Consult your site developer if you need further explanation about this feature.