Bixby is a Virtual Assistant by Samsung, same as Google Assistant and Alexa. You can ask to open Cetain apps, ask weather, to make a call, say news, and give other voice Commands for it to make the job done for you. It can do almost same stuff that other Voice Assistant do, but for Samsung Devices it can do more stuff that other Voice Assistant aren't able to do. For newer devices of Galaxy Flagships like after S9 line, you can add quick command, that you can set it up for faster and easier performance. For more info you can see this links:
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