How to correctly define the necessary events and filters?

Question

WordPress

I'm not familiar with wordpress))) I'm trying to understand how it works...

When I want to make changes to a plugin, how can I easily find the necessary filters and events to which I should bind my functions?

And another question, how can I access the database and is there something built-in to work with js, for example, execution without a page refresh?

Thank you!

Answer 1

Where to look? Documentation.
It is better to access the database through the WordPress API, if something is standard, such as adding a post, making a new post type, etc. - there are ready-made functions. If it has its own logic - the global object $wpdb.
Without a refresh, this is ajax, you can make your own handler, or you can use the REST API, which can be extended.