Since you're making a living with Odoo, your family's and your life depends on it, maybe you'd approach it more seriously:
1. Read all Odoo developing documentation.
2. Watch all development youtube from Odoo experience.
3. Read through all the OCA modules to see what they look like.
4. Buy some Udemy development course
5. Read Odoo development book. At least some free one (I believe Cybrosys has one [https://www.cybrosys.com/odoo/odoo-books/odoo-16-development/]). 
6. Study all the HR related modules (from enterprise, from OpenHRMS, from other 3rd party providers to really know what to do, how to do, how to make sure the code do what it supposed to do etc.

Making a module is as simple as a odoo-bin scaffold or a ChatGPT: generate me Odoo module. Making it works at enterprise level is another story.