GRASS stores data in the form of location and mapset. Location Wizard avaialble in Startup will allows to create your own location
A location is defined by its coordinate system, map projection, datum and geographical boundaries. The subdirectories and files defining a location are created automatically when GRASS is started the first time with a new location. Different location have its own CRS defined by user.
Each location can have any number of mapsets. A Mapset is a location’s subdirectory. A new mapset can be added at GRASS startup. A default mapset “PERMANENT” is automatically created when creating a new location.
Once the Location/Mapset is created you can import raster map using File Menu.
File -> Import raster data -> Coomon formats import [r.in.gdal]
Importing data without knowing location information
The above method will only work if you are aware of the projection, datum and geographical extent of the data you have. If you only have data and need to import into GRASS for visualization and do further analysis, GRASS allows to create a new location from the metadata associated with the raster maps. For this you need to setup a arbitrary location xy using location wizard or open up a location in sample data available from here.
From GRASS shell issue the command r.in.gdal which shows up a dialog shown below
Specifying Optional Parameters
Restarting GRASS into new Location
select newly created location “mylocation“. You can see a default mapset “PERMANENT” is created automatically
Your new map is already available in the mapset. You can view it using Layer Manager for visualization