Unique List Permissions
You can decide to break this inheritance and give unique permissions to the list. This is most common when working with lists that contain sensitive information that not all site users should see. Another example is a list that all users should have the ability to update, even those site users who normally have only a Read permission level.
To break permission inheritance for a list, perform the following steps:
1. On the list page, select the List Permissions command from the Settings group on the List Tools - List ribbon.
2. On the Permissions screen, select the Stop Inheriting Permissions command from the Inheritance group on the Permission Tools – Edit ribbon.
3. On the confirmation message, click the OK button.
Once these steps are completed, you will be able to manage the permissions levels for users within the list. At any time, you can revert to the site’s users and permission level security by selecting the Inherit Permissions command from the Inheritance group on the Permission Tools – Edit ribbon.
As an administrator, you have many options for changing list permissions. Access can be granted based on SharePoint groups or domain users and groups.
To add users to the list security, perform the following steps:
1. On the Permissions page, select the Grant Permissions command from the Grant group on the Permission Tools - Edit ribbon.
2. On the Grant Permissions window, enter the e-mail address or account name of one or more users or groups you wish to add in the Users/Groups box. You can verify that the information you entered is correct by clicking the Check Names icon.
3. If you do not know the exact e-mail addresses or account names of the people or groups you want to give access to, you can click the Browse icon. This icon will open a window that will allow you to search for accounts within your organization. When you have found a user you wish to grant list access to, select that user in the list, and click the Add button. After you have done this for all of the users and groups you wish to add, click the OK button.
4. Select the permission level that you want to use to determine your new users abilities in the list. These permission levels are managed in the site.
5. Click the OK button.
You will now notice that the users you have added show up in the list of users on the Permissions page. You can edit the permissions of a user or group by checking the box next to the name and selecting the Edit User Permissions command from the Modify group of the Permission Tools - Edit ribbon.
Likewise, you can revoke a user’s access to the list by checking the box next to the name and selecting the Remove User Permissions command from the same ribbon group.
If you have any doubts or queries regarding the above mentioned information then please let me know,Thanks...