Last October, I had the honor of making such contact with the ISS. I posted about this on my website here: https://rz01.org/na1ss/

The ISS has radios on board that allow amateur radio operators to send and receive APRS messages, talk to other hams via their built-in FM repeater or to receive SSTV images. They also have amateur TV stuff on board but I have not explored this yet. Crew members with an amateur radio license can pick up the mic of the radio that acts as a FM repeater to make contacts with other hams on the earth.

You can contact the ISS via a handheld setup (FM radio and a yagi antenna in your hand) or with a stationary setup like mine: https://rz01.org/leo-sat-ground-station-v3/