Allow specific HTML tags inside a text field of a custom content type using CKEditor
I can't figure out how to &quot;connect&quot; an editor format to a field and
make it selectable for the one who adds a field to a content type.

The text formats are shown in order here:
/admin/config/content/formats
The format at the top of the list is the default format.  To change the order of the formats, drag the arrow icon on the leftmost side and then press save.
Users can only see formats for which they have permission. The roles with permission are listed in the Roles column of the table at /admin/config/content/formats.  To change the permissions, click &quot;Configure&quot; for the relevant format and add the correct roles.