Hi,
how to add the search bar depends mainly on your theme or the page builder you are using, as far as the code that generates the search bar goes you can use the [adverts_list] shortcode like this
[adverts_list search_bar="enabled" show_results="0" redirect_to="https://example.com/"]
where https://example.com/ is a link to a page with the [adverts_list] shortcode that can show the search results, or you can just use a simple HTML form like this
<form action="https://example.com/" method="get">
<input type="text" name="query" placeholder="Keyword ..." />
<input type="text" name="location" placeholder="Location ..." />
<input type="submit" value="Search" />
</form>
