Setting item level permissions was straight forward in SharePoint 2010, you selected the items you wanted to break inheritance on and selected the Permissions item. When moving to SharePoint 2013 and trying to do the same thing, to a lot of users this functionality appears to no longer exist. Worry not!
To set item level permissions for an item (or multiple items) select the candidate items and switch to the Items tab in the ribbon.
Notice the ribbon item called Shared With. This is what replaces the Permissions item from 2010. Click it and a list of users that the item is shared with loads.