I need to get some functionality that is only available by using php. I am currently learning php and wordpress back-end so this isn't a major issue (although tbh plugins that require coding to use kind of defeats the point of a plugin in the first place, imo).
I am also using Oxygen Builder so the theme is disabled. So if I was to use code to create my post types and fields groups - where do I put my code? Is the only option to create a custom plugin?