One of the features in SharePoint is the ability to grant users access to different parts of the site. Once you do this however, it can become difficult to manage. Thankfully there are some great quick tools that are included that allow us to quickly identify the site permissions structure.
The first feature is the notification that some of the content in the site is uniquely secured. This is displayed on the site permissions page in a yellow menu bar. If you don’t see this menu it means that all the content in your site inherits permissions from its parent:
When you click this link, another screen opens and shows you what lists have had unique permissions applied.
The other feature I found helpful, was the Check Permissions option. When you select this you are able to enter a username and it will display for you if that user has been added directly to the site or if they have been placed in a group.
Here is one for a user that was added directly to an item:
These features will allow you to quickly identify content within your site that has been uniquely secured. You can also use these tools to find the current permissions for any given user. This is definitely the first place you should look if you have any issues with users accessing your site.