Madison,

          If you're talking about managing a calendar or calendars under the Google web interface, that's never been done in the Gmail interface, although you can put a calendar sidebar there.

          If you want to manage calendars under Google then, once you have logged into your Google account for any of the services, you can either activate the apps button at the top of any given service's page, find the other app you need (Calendar, in this case) and activate it or you can just paste the calendar app URL into a new tab:
https://calendar.google.com

Then you'll have to deal with all the settings specific to calendar to get the display format you want and to have the calendars you have access to either have appointments be displayed or not displayed.

All settings for a calendar or calendars for a given Google account, including who they're shared with, are handled under the Calendars interface under settings, specifically the section, Settings for my calendars.

There are multiple help pages and tutorials on using Calendar with a screen reader:  https://duckduckgo.com/?q=Google+Calendar+screen+reader 

The general principle here applies to any Google app:  Contacts, Calendar, Drive, Gmail, Sheets, Docs, etc., all have their own dedicated web interface where sharing for those things is managed, even when that sharing is across multiple Google accounts.  The owner for any given thing controls who else may access it, and they control that through the interface for the thing being accessed in its sharing settings.
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Brian - Windows 10 Pro, 64-Bit, Version 20H2, Build 19042  

It is better to be hated for what you are than to be loved for what you are not.

           ~ André Gide