NOTE: by default, everyone's calendar is already shared with the basic viewing settings. You will only be able to see if the user is Free or Busy. Follow steps below to grant more detailed options
1. Right-click on your Calendar > Properties
2. Click on Permissions tab > click Add and search for the user you want to grant more permissions too
3. Change Permission Level to Reviewer. This will allow the user to see the full details of everything on your calendar. NOTE: It is not recommended to give anyone Create/Edit or Delete rights to your Calendar.
Related Articles:
- How to add Shared Calendar - https://smolin.freshservice.com/support/solutions/articles/4000058605