Sharing permission on a SharePoint Online Folder

Hello Pradeep Kandel 

when you have private teams, only the members and owners have access to the files. When you have public teams, everyone in the organisation have access to the files.

You can also create private or shared channels in teams, with these, only the members in this channels have access to the files.

Otherwise in SharePoint you can stop inheriting permission and you can set specific permissions for folders: https://sharepointmaven.com/how-to-create-unique-permissions-for-a-file-or-folder/

Best, Dave