There are countless guides online, just search ‘WordPress Theme creation’ on Google.
A good place to start would be https://www.dreamhost.com/wordpress/guide-to-developing-a-wp-theme/
For folder structure I suggest you use a ‘WordPress Theme Boilerplate’, you can generate one here: https://underscores.me/, but there are loads of other options. More are listed here:
https://www.wpbeginner.com/wp-themes/21-best-wordpress-starter-themes-for-developers/
Or if you don’t know php, you could try this:
https://www.wpbeginner.com/wp-themes/how-to-easily-create-a-custom-wordpress-theme/
Entering the question you have asked here on Google will give you many more results which might fit your needs even better.