Explanation
You can choose from all objects-even those you don't have permission to view. This lets you buildreport types for a variety of users.Once you save a report type, you can't change the primary object.If the primary object on a report type is a custom object, and the custom object is deleted, then thereport type and any reports created from it are automatically deleted.If you remove an object from a report type, all references to that object and its associated objectsare automatically removed from reports and dashboards based on that type.http://help.salesforce.com/apex/htviewhelpdoc?id=reports_defining_report_types.htm
&language=en_us

Hierarchical relationship: This type of relationship is a special lookup relationship available only for the user object. It allows users to use a lookup field to associate one user with another that does not directly or indirectly refer to itself. For example, you can create a custom hierarchical relationship field to store each user's direct manager.

Explanation
Groups Appears for organizations that have Chatter enabled. If you don't add this item to the navigation menu, groups are automatically included in the set of Smart Search Items instead and the Groups item is available from the Recent section.
https://developer.salesforce.com/docs/atlas.en-us.salesforce1.meta/salesforce1/customize_s1_nav_about.htm