Report builder is a browser based report authoring tool to enable any end users to start building / modifying existing reports (if they have enough permissions) without the need of any installation of BIDS or SSDT. This tool is available via local installation of Report manager. This is a light weight tool that will enable you to definitely build a decent report and you can deploy it directly to the report manager. You can start building this report against SQL Server database, SQL Azure, Oracle and others. Below image also explains more on Report builder tool and also try watching a quick video on this here.