The Report Wizard enables users to build basic reports without development knowledge by providing an easy-to-use interface for doing so. With Microsoft Dynamics CRM 2013, reports are generated using native Fetch-based queries through the data source (called MSCRM_FetchDataSource) found in the Report Manager and available to support Fetch queries.
In addition, the final reports are actually Microsoft SSRS reports, or .rdl files, which you can further manipulate using a more advanced editing tool such as Visual Studio, provided you have Report Authoring Extensions installed.
As with earlier versions, reports built with the Report Wizard can be edited using Visual Studio. This is usually done to increase performance, layout, ...