Define User Managed Sharing in Salesforce?

Hi Shubham,

You can control whether the Sharing button is displayed on user detail pages. This button enables a user to grant others access to the user’s own user record. You can hide or display this button for all users by following these steps.

From Setup, enter Sharing Settings in the Quick Find box, then select Sharing Settings.
Click Edit in the Organization-Wide Defaults area.
Select the Manual User Record Sharing checkbox to display the Sharing button on user detail pages, which enables users to share their records with others. Or deselect the checkbox to hide the button, which prevents users from sharing their user records with others.
Click Save.
When the organization-wide default for users is set to Public Read Only, users get read access to all other user records, can see those users in search and list views, and can interact with those users on Chatter and Communities.

Thanks