By default, all sub-sites, lists, and libraries within a site inherit permissions settings from whatever is directly above them in the site hierarchy.

For example, a list item inherits permissions from the list that it is in. A list inherits permissions from the site is on. In each of these cases, the content from which permissions are inherited is called the parent.

In some cases, your site might contain content that’s only meant for certain users or groups. 

For example, if you have a list on your site that contains sensitive data, you might want to restrict who can see it. To do this, you break permissions inheritance, and then edit permissions for the content on its own permissions page.

Break inheritance from the parent:

1. Open the list that you want to restrict access to.
2. On the List Tools tab, click List to open the gallery of commands specific to the list.
3. On the ribbon, click the List Permissions button.
4. Click the Stop Inheriting Permissions button.

Here are two important things to note:
- The list still has the same permission settings that it did before. But now, instead of inheriting permissions from the parent, it has its own copy of the parent’s permissions. 
- Changes that you make to the permissions settings for the parent site will not be inherited by this list.

Remove groups or users you don’t want:

1. In the Name section of the permissions page, select the checkboxes for the groups or users who should not have access to this list.
2. Click Remove User Permissions.

Grant access to groups or individuals:

1. On the permissions page for the list, on the Edit tab, click the Grant Permissions button.
2. Type the name of the group or the individual you want to grant access to in the Users/Groups box.
3. Choose the level of permissions you want the group or individuals to have.
4. Click OK.

Reconfigure a list to inherit permissions:

After you’ve broken permissions inheritance between a site, folder, list, library, list item, or document and its parent, you can restore inheritance at any time. 
1. Open the list that you want to restore inheritance for.
2. On the List Tools tab, in the List gallery, click the List Permissions button.
3. On the list permission page, click Inherit Permissions.