Theory knowledge and impro lessons by: David from piano-play-it.com
Hi Juliana,
You have asked to gigantic questions :) I love your curiosity. Both questions by the way have to do with you wanting to know more about music theory and how to implement it practically.
1. About your question on getting to know to learn to find the harmony of a song. Click here to inestigave this issue: https://www.piano-play-it.com/piano-chords.html
Start from reading about chords theory. Once your'e familiar with the basics wait for the piano course I'm going to create, teaching you how to find harmonies for songs.
2. As for improvising, byt getting to know the piano chord theory stuff you'll be able to find the skeletones for creating a great accompaniment. I will create a piano course regarding that issue soon enough as well so stay tuned.