This forum is so BUGGY, i have tried to answer as close as possible (temporary posted it as reply to my own answer), as I was still ending up with 403 error. I have found the reason - LINKS - this forum editor will throw 403 error every time you post a link. Please odoo guys, fix this...

MY ANSWER TO YOU
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I can only recommend you books which will help you learn to do that. This is to much job to explain it here in a single post, step by step. So my advise is to:

1. check the API documentation, it almost always contains some examples for different programming languages
2. then start from creating new odoo module, manually (if you now the scheme) or using the scaffold parameter of odoo-bin like this:
   

   1. /odoo/odoo-bin scaffold my_new_module_name

3. This will results in creating your new module structure with template files which you should start to fill.
4. Now please use odoo docummentation or one of good books/ebooks on the market like "Odoo 14 Cookbook" or whatever versio of Odoo, depending on which are you working with.
5. 1. odoo.com/documentation/15.0/developer/howtos/backend.html
   2. odoo.com/documentation/15.0/developer.html
   3. packtpub.com/product/odoo-14-development-cookbook-fourth-edition/9781800200319 - need to by but there is also a subscription version of this ebook online, you can use a 10-day trial to continue reading
   4. subscription.packtpub.com/book/big_data_and_business_intelligence/9781785883644/3/ch03lvl1sec30/using+scaffold+to+create+a+module

Take it easy, go step by step and google every aspect you do not understand.This is what I can recommend to you for now, as I have an impression, you have just dived in odoo development. Probably noone have so much time here to help you, ad this takes priceless time. Good luck, buddy! Do not give up. Take this as your challenge. 😎 😎 😎

Regards