Child themes

Hello,

I am all new to building websites and wordpress and so please accept my apology if this question is really stupid. I have tried to search the net and youtube but I am unable to fully understand the solution and how I should incorporate it when I start building my site. I have zero experience and so please bear with my ignorance.

As far as I understand if you make changes to a theme that involves direct editing of the code (not using the choices given in wordpress to eg. change pages etc) then it is advised to make a child theme.

I saw a video using child themify to produce a child site (https://www.youtube.com/watch?v=HrkyieFkk4g) . But then what ??

How do I get the changes to my website to appear in both the parent and child theme ?

When the page is running on a day to day basis should it then run parent og child theme ? And when an update is released, then what ? Will the presence of a child theme avoid loss of my editing of the page or will I have to do something active to regain my changes to the website ?

I hope my questions makes sense and I really hope that you can help med since I really want to try to learn and make my site.