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Hi there, thank you for the help in advance.
I would like to find out where can I learn more about storing and retrieving custom data in WordPress. For instance, a website can store the information provided by a user. This information can be then displayed on the website for everyone to see.
I want to avoid using plugins or third-party software.
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Why no plugins? Are you going to write code in a custom or child theme?
Learn about how to use the RestAPI and you’ll be able to store and retrieve data to your hearts content. Not only inside of WP but from any database or third party service.
You can review the add_post_meta() and get_post_meta() functions on the WordPress Codex. What you are looking to do requires development knowledge (HTML forms, wordpress hooks and filters, wordpress PHP functions or alternatively the REST API as another commenter suggested, which means knowing javascript and ajax methods within the WP ecosystem).
Custom Post Types & Custom Fields (ACF Pro is the best, if you can utilize strong plugins)