Answer 1

To give you a simple answer - it is a way for the machine of solving problems algorithmically, without being explicitly programmed to do so :)
https://www.sololearn.com/learn/714/?ref=app

In practice - it is making an algorithm digest some past data in order for it to be able to predict future data.

Check it out:

https://code.sololearn.com/cU8787JuqEmN/?ref=app
https://code.sololearn.com/cwstTU4ohOr9/?ref=app