Need help understanding child theme capabilities please

Hi – hoping to find a kind person or two to help me quickly understand some nuances of child themes.
Background:
I am not a programmer. My site is hosted with a third-party hosting provider. I have a plugin (currently not activated), called One Click Child Theme, that will create a child theme for me.

Current situation:

• I have made modifications directly to my theme. These changes have been made to index-one.php and functions.php
• My theme has come out with an update.
• I have recorded the theme changes and can easily make them again, but even “easily” takes 30-40 minutes, and I have active traffic on my site. The changes are small but have a big impact.

I’m looking for an easier way.
My question:
If I make a child theme from the main theme right now, will the child theme contain the code changes I made in in the main theme?
My next question:
Does a child theme automatically get updated when the main theme does? If yes, how does it not get the changes overwritten with the new files?

I was thinking that I could use the child theme almost as a backup, so when an update comes out, I make a new child theme, switch the site to it, and do the update on the main theme. Then I could make the changes to the main theme and switch the site back over to it when complete.

Does any of this make sense? I just want to do this in the best way so that visitors to the site don’t see the stuff I cured with the small changes I made to the files.

My theme is AccessPress Lite. If I do the update without trying what I’ve outlined here, the events on the main page will go back to default (which is bad), the welcome post will look like a post excerpt, and something odd will happen with my events (managed by plugin The Events Calendar).

I currently have a minor theme conflict with The Events Calendar plugin that I am hoping has been cured by the latest update; thus my urgency in understanding this.

If you’ve read this far – THANK YOU. I probably provided more details that you need, but better to have too much than too little, right?

All assistance is very appreciated.
MJ