This is interesting question and people don’t really know!
There are a few theories though:
From the outside looking in, if your friend were to go into a black hole it would look like they were slowing down. Once your friend is in the black hole, it will look like they have frozen in time to you!
Your friend however, it’s going to be a wild ride for them. They’ll be stretched out due to change in gravity, called spaghettification. Light moves in a circle when it’s trapped in a black hole. This means you’re friend will be able to see the back of their own head! What’s more, as they spend longer in the black hole everything will get bluer and bluer!
Some very smart computer scientists have recently made a virtual reality tour of a black hole. Hopefully this will be put on VR headsets in the near future: