Bixby is one of those AI apps that can do all manner of things for you (like Siri, Alexa, Google) by speaking to it, and it can do some kind of optical recognition of pictures, etc. However, if you don't want to use it, having it accidentally pop up and get in your way, is an ongoing annoyance. If you swipe the main screen to the left, it's there. If you press the Bixby button on the side of the phone, right where you're likely to grab the phone, it pops up.
This can be disabled, but I couldn't manage to do so until after I'd allowed it to run, which included creating a Samsung account (which then rifled through my contact list and copied them, which needed fixing up later).
Once run, you can switch it off from being activated by the Bixby button on the side of the phone - there's an on/off slider on one of the starting pages, that deactivates that feature.
You can stop the Bixby home appearing when you swipe the screen. Hold your finger down on the main screen until you get the screen editor. The main screen will shrink down, you'll get some functions appear below. You can swipe left where the Bixby screen will be, and toggle the on/off switch. And you can swipe right to where extra home screens may be, and delete them (there's no point having them if you're not using them).
Bixby can still pop up through other things, but you're not going to accidentally get it just handling the phone, after those steps.