Alright, You did not mention if that data will be stored upon submission from front end or you want to manually put that in. But lets see the way I would handle form submissions and store email addresses. I would use contact form 7 along with its addon Flamingo. It will let you store all the email submissions made through the contact form. I hope that is the flow you are looking for.
Also, to insert something into wordpress database, you need to write a simple query, such as:
Put This Inside your functions.php
global $wpdb;
$insert_into_database = $wpdb->query($wpdb->prepare('INSERT INTO your_table_name (column1,column2) VALUES (%s,%d)',array($value_1,$value_2)));
if($insert_into_database){
// Do something on successfully inserting data.
}
Also we are using $wpdb->prepare to prepare our sql for safe execution.
%s – string (value is escaped and wrapped in quotes)
%d – integer
%f – float
%% – % sign
I hope this solves your problem! Cheers 🙂