upload code for new gallery or install plug in

Hello,

I am using a child theme of mystile. I do not have a developer and do content edits myself. Never had a need to go into WP files. Now since the WC 3.0 and up does not have the gallery function anymore, unless using a default theme, it sound like you have to either upload some code into your function.php file or install a plug in.

I found these two articles one on how to write code to your function.php and one on best to not add code to your WP files. I have never opened or edited any .php files. I have Bluehost as my hosting provider and do know where my files are though. Any suggestions on for someone with little knowledge of editing .php files or should I find a plug in for a gallery function. Any advice is appreciated.

https://managewp.com/edit-wordpress-website
https://createandcode.com/broken-photo-gallery-and-lightbox-after-woocommerce-3-0-upgrade/
http://wpninjas.com/stop-adding-code-functions-file/

Also if you see anything that is incorrect in the articles that would be helpful as well. Thank you.