If you would like to give a person permission to access a folder in your Microsoft 365 account it involves giving permission in two places. First, you need to give the person permission to access your Microsoft 365 e-mail account Mailbox (e.g., Mailbox - Doe, Jane) then you need to give the person permission to access each Folder/Subfolder you want to share. The process for sharing your Mailbox and your Individual folders is the same.
If you are trying to share your entire calendar with other users (and not just one particular folder or calendar) see Sharing Your Office 365 Calendar for instructions.