How to work with wordpress data in php?

Question

WordPress

I decided to write a php plugin that will take information from the meta fields I created,
then transfer it to RSA encryption and then write it to the SQL database.
But since I'm a total newbie, I have a couple of questions:

Which function pulls data from meta fields for further processing?
Which function sends data directly to a SQL database?

Answer 1

Working with post metadata:
https://developer.wordpress.org/reference/function...
https://developer.wordpress.org/reference/function...
Working with the database directly:
https://codex.wordpress. org/Class_Reference/wpdb