now I understand. Before you open Sentinel-1 data in any GIS you need to pre-process it. It is neither calibrated nor projected in the .SAFE format and cannot be used right away. For GRD products, the minimum steps are listed here: Radiometric & Geometric Correction Workflow
Once you processed your data, it will be written in a BEAM DIMAP format. This is how SNAP handles the raster and metadata of the product. It consists of a *.dim file and a *.data folder. In the data folder, there are hdr files and img files and the latter can be opened in QGIS. But you need to terrain corrected data for that.