Over on YouTube user ModernHam has uploaded a useful tutorial showing how to use our RTL-SDR Blog V3 dongles for FT8 monitoring. The RTL-SDR Blog V3 has a built in direct sampling circuit which allows for reception of HF signals without the need for any upconverter. FT8 is an amateur radio weak signal digital communications mode which can be received all around the world even with low transmit power.
In his setup he uses SDR# and Virtual Audio Cable to pipe audio to the WSJT-X decoder. His video goes through all the steps and settings that need to be set and then shows a demo of some signals being received. ModernHam also has another video uploaded a few days earlier which is a more general introduction to FT8 decoding.
If you're interested we uploaded a tutorial last year that shows how to set up a Raspberry Pi 3 based FT8 decoding station with a V3 dongle.