Your site may have contents that should be restricted to certain users or groups due to the level of sensitivity. To do this, you break permissions inheritance, and then edit permissions for content on its own permission page.
i. Break inheritance from the parent
1. Open the list that you want to restrict access to. Go to [List Tools] tab -> click [List] to open the gallery of commands that are specific to the list.
2. Click [List Permissions] on the ribbon. (You will receive a yellow status bar that explains that the list inherits permission from its parent site.)
3. Click [Stop Inheriting Permissions]. (The list still has the same permission settings that it did before. Now instead of inheriting permissions from the parent, it has its own copy of the parent’s permissions).
ii. Remove groups or users that you don’t want
1. On the Permission page, go to Name section. Select the checkboxes for the groups or users who should not have access to the list.
2. Click [Remove User Permissions].
iii. Grant access to groups or people
In case you want to create a group and grant it access to this list or may want to grant access to one or two people on your team, follow the below steps.
1. From the permission page, click on the [Edit] tab -> click [Grant Permissions].
2. Type the name of the group or individual you want to grant access to in the Users/Groups box. Click [OK].
iv. Reconfigure a list to inherit permissions
1. To restore inheritance, open the list that you want to restore inheritance for.
2. Go to [List Tools] tab, in the List gallery, click [List Permissions].
3. On the List permission page, click [Inherit Permissions].