Save and retrive data from a custom form to database

It’s totally depends on your sow. You can choose custom table to insert custom data and that’s need so much code like mysql query to insert data and fetching data using the same approach. If you feel comfortable with those approach you can look for wordpress WPDB.

But to me if you want to build a system which store data from the custom form and stores on the table and display on the wordpress admin panel as well then you might need to go with wordpress default conventional tables. By using custom post type. In this way you can easily display the stored data in the admin dashboard as well as admin can easily change , delete it. And that’s a default features.