https://webdesign.tutsplus.com/courses/customizing-wordpress-with-child-themes
Customizing existing WordPress themes is a great way to get the look you’re going for, but if you’re not careful, when you update your theme, you can easily lose all of the customizations you’ve made. In this short course, you will learn how to use child themes to customize your WordPress websites, so you can make all the changes you want without worrying about losing them.