See the documentation here.
https://wpadverts.com/documentation/custom-fields-paid-addon/
I was in trouble too after reading it worked out.
Form – Search
When you will create first search form you will notice that it layouts differs from the Ad form and mimics the design of a search form in [adverts_list] shortcode…
Taxonomies
Taxonomies usually have predefined values in the wp-admin panel, so most of the time you will want to use radio, checkbox or drop-down inputs to search for them, although the search can work with other inputs as well.
By default the sentence will look pretty much like below, you will need to fill two values:
In the first field you select taxonomy field you want to search by, allowed values are term id, title, term slug and term taxonomy id. When searching by “Adverts Categories” you will want to select term id, in other cases, it will depend on how is your callback function was written or what field you are using to search. If you are using a text field it makes sense by title or term slug….
