Is it possible to put a post in a section?

By sections you mean a post category or a CPT taxonomy? In which case don’t add any default labels to your dropdown and simply map it to an existing taxonomy.

I mean the category of posts. How to do it, please?

that’s what I explained in my reply,

In which case don’t add any default labels to your dropdown and simply map it to an existing taxonomy.

see the plugin’s youtube tutorial on mapping submissions to taxonomies

Thank you so much!!