how to send demo or proposal to website visitors who wrote their email address on input form?

I've been making new website for my company. I'm a new employee and here are my questions.

1. How to send demo file or proposal automatically to visitors who wrote their email address on input form?

2. Where could I get some codes for it using web-hosting service? Would you please leave some URLs or websites to get plugin, codes, templates?

3. Where could I get some codes for it using own DB(MariaDB)? Would you please leave some URLs or websites to get plugin, codes, templates?