How to copy existing theme so it doesn't mess up when updated?

Ok I am a newbie and learning as I go for the last week. I have wanted to develop my businesses own website for the knowledge and savings. Anyways this might be right in front of my face but. I have almost got my website finished and have little knowledge about how child themes and original themes work. All my custom coding and plugin manipulations have been on the Woocommerce Storefront theme. Not a child Storefront theme but the Original. I have read that all my work will vanish when the theme owner updates (If I am correct). Anyways I have the plugin child themes and have messed with it a bit but the child themes look nothing like my original. How do I back up the original so all my time is not just gone one day? Thanks ahead!