Loading raster files is not much different from loading vector files. Selecting the menu entry Layer and then clicking on Add Raster Layer, clicking on the Add Raster Layer button, or pressing the Ctrl + Shift + R shortcut will take you directly to the file-opening dialog. Again, you can check the file type filter to see a list of supported file types.
Let's give it a try and load landcover.img from the sample data raster folder. Similarly, just like vector files, you can load rasters by dragging them into QGIS from the operating system or the built-in file browser.
Note
Support for all these different vector and raster file types in QGIS is handled by the powerful GDAL/OGR package. You can check the full list of supported formats at www.gdal.org/formats_list.html (for rasters) and www.gdal.org/ogr/ogr_formats.html (for vectors).