Is Demo data at risk

I’ve installed your demo data and I’m adding pages, changing the menu content, modifying existing pages etc. I’ve heard about a child theme, but don’t fully understand if I’ll need to change my site. Somebody suggested that when your team sends out an update it will overwrite everything I’ve done so far. Is this true? If I do need to put my existing site into a child theme … how would I do this (I’m not a coder) so it’s got to be brain dead straight forward.

thanks.