If you wish to make a newslatter module, then you need to write code for this. I’m explaining this below.

Add HTML form to view newsletter module
Add Database Table (Migration)
Add Model of that table
Add Controller to write the logic

Set action from HTML form to your route,
the route should hit to your newsletter controller to save necessary information

Show your added newsletter information to admin

Hope it will help you

Actually, it’s the lot of jobs you need to be done to make this module.

Or you can add any embedded code from newsletter service like MailChimp

Best Regards