I have in the same folder .tif and .twf files with the same names. How should I open them in QGIS correctly? If I select add raster layer and add the .tif file, would that be enough? Would QGIS also consider the .twf file? And how can I understand if it is correctly geolocated?
Yes, it's enough.
.twf is the world file for
QGIS will read it when you open your
.tif raster file.
Use a basemap like OpenStreetMap or other vector files that describe lands, countries, etc. located at the same place as your
.tif for verify the location. OSM is configured by default, look at this for find how to open the OSM basemap (XYZ Tiles in the Browser Panel).
Or just check coordinates, if you know them. You can use this kind of site to verify the coherence between coordinates and CRS (coordinate system).