What are IVRs with speech recognition?

Question

Speech recognition

I'm generally new to IVR, just now I need to do something like this: there
is a call, the user is speaking, and depending on the context that he said, I have to turn on the desired audio. Those. the user says "hello", I let the record responsible for answering "hello". If he says something that is not clear, I include "I do not understand you." The important thing is that here it is necessary to insert your own audio, and not the speech of the computer.
How can this be organized?