How can we handle the custom field in wordpress mean which db tables involves and which hooks we use to store custom fields?

Displaying custom field:

for example to display custom fileds to each post use the the_meta() template tag.

the tag must be put within the loop in order to work

<?php the_meta(); ?>

https://codex.wordpress.org/Creating_Tables_with_Plugins

you can see this website

The custom fields are stored in this table of WordPress wp_postmeta.  $wpdb->postmeta

For displaying you can use this, custom fields to each post use the the_meta() template tag.

the tag must be put within the loop in order to work

<?php the_meta(); ?>

e.g.