posting post from front end

hi i am trying to create a theme in which user can post content from front end for doing show i am the code

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i am find these code from
https://wpshout.com/wordpress-submit-posts-from-frontend/
this site my froblem is that i want to add a custom field value with post so i am using add_post_mata() function . but in this function how we can pass post->ID parameter to add custom field value in this post.

please help me ?
i am intermediate knowledge in php .
i really appreciated your answer .