My difficulty is in understanding how to perform this very basic functionality in Wordpress. I have used form builders like Ninja Forms to graphically build a form creating a form with text fields for user email and password and also a submit button. I was able to have this form successfully displayed on my Wordpress site and performed a test on this form. The form submission was successful and the data from the form scenario results in an email being sent and/or being recorded in the "Submissions" area of the forms tab within the wp-admin dashboard.
What I can't figure out is:
1) How can I grab that information (user email address, password) programmatically so I can query a non Wordpress table.
2) How do I integrate custom PHP pages into my Wordpress site. I used a plug-in called "Insert PHP" where I use special delimiters to include an actual .php file in a page created in the wp-admin dashboard but this seems like a clunky solution. I read up on Wordpress tutorials and I understand that posts, pages created in the wp-admin dashboard are not actual files so I can't just go to the source code of those posts/pages and customize them. I also read that I just can't go into the Wordpress file directories to hack Wordpress core files. I also read that for some complex functionality, it may be required to write a plug-in myself to handle more complex situations. However I think I am missing something basic as I wouldn't think getting some data out of a form and querying a MySQL DB should be that hard to necessitate writing a plug-in.
Thanks in advance for help.