How to use has_many ActiveRecord?

Question

Ruby on Rails

Hello, please tell me how to use has_many to link several comments to one post in an asset record, I will be very grateful for the example. It turns out that the posts are saved separately, and the comments are saved separately, the post_id field always remains empty, therefore the comments do not correspond to any post. How to correctly accept parameters and save them so that there is a match?
PS: please don't link to guides.rubyonrails.org , didn't find an answer there