I'm not a Siemens guy but I just had to do this very recently.
Open up your project in TIA Portal, go to 'Devices & Networks'.
Up top click on Options > Manage general station description file (GSD) and browse to your downloaded GSD files.
After this, whilst still in 'Devices & Networks' you can open up the hardware catalog on the right and browse to the new devices you added, then drag and drop them onto the network view to configure.