WordPress works with themes. A theme is the one that defines the look, feel and structure of your website, it includes templates of the different type of pages your website can use, the styles of the fonts and colors in which the content will be presented. It also includes the functionality to it.
A Child Theme is a theme we create based on the main theme, but it allows us to re-write some features and functionality of the original one without modifying its source code.
When we create a Child Theme, we are able to modify selectively, modify the layout, styling and functionality without major consequences in the original code.
It will still follow the guidelines and work as its parent theme, but it will be able to have unique customized features that will help you create a different version of that theme. For example, you find a theme that you love online but you wished its colors and fonts were different and that the sidebar was on the other side of the screen. This is easily done by creating a Child Theme and re-writing the instructions from the parent theme that specify the colors, fonts and position of that sidebar.
I insist and persist that when working with WordPress you always create a Child Theme and work from there, that way, anytime an update of the parent theme is released, you don't loose your customizations by updating the source files, and will not corrupt the original parent by changing the source code. Keep the source code as it is, and build your customizations based on it.
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