This blog may help you to understand about the SharePoint Permission and how we can make a folder or document library with unique permission.
First let us see, how the permissions work in SharePoint at Site Collection Level

- Full Control: Can do all the activities within a site or site collection
- Design: Can view, update, delete the document and can customize the SharePoint page
- Edit: Mostly this permission user can add, edit, and delete the document, folder, and list item
- Contribute: same as edit permission
- Read: this user can only view the item and document, can note edit or delete and can download
- View Only: same as read permission but user could not download any document
Site Title Owner – Mostly have the full control
- Site Title Member – will have the contribute or edit permission
- Site Title Viewer – will have the Read or View permission
Initially, the SharePoint Permission group will create at parent site, and will be applicable for all child items like sub-site, list, document library, documents, and items.

This concept is called Permission Inheritance, whenever you change something at parent or child level it will synchronize or reflect on both.
So now let us see how to break the SharePoint Permission group and make a folder with unique permission
First, I am creating one Document library in my site collection and I am creating one folder called unique (as of now that folder inheritance the permission from parent, which means from site collection)



Now you can see below that indicates, the folder has unique permission. Now you can remove everyone from the folder permission group and add those who are required to access that folder
Now only that person can see and access the folder, who has been added to the folder permission group. Remaining users can’t see that folder in the document library (just hidden from their view)
Again, if you want to make that folder visible to everyone just click delete unique permission from left top of the ribbon and it will again join to the parent permission.

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