Add and Read data to and from custom table

I am trying this for the last 2 days in various ways without any success.
What I want to do is . . .
Collect data via a form from the end user and add it to a Table under WP database on form submission. My from processing code resides in template dir/files/process.php

I like to use the global $wpdb here!

Then I want to list the submission for moderation with buttons <Accept> <reject> or <edit>

on Accept the data should be posted as post to WP. This can be done via add_post hook.

But All of them are not failing into place.

Is there a simple sample code with examples for this kind of purpose?

After all I realize the hooks are powerful but documentation is not that well like template docs.
Appreciate any help.