Create template which shows listings with a particular custom field

I thought I could figure this out, but am stuck.

I need to create a new template for a page which will list all listings that have a custom field in map-city such as Cincinnati.

I think I am getting somewhere with WP_query shown in the link, but I am stuck: https://codex.wordpress.org/Class_Reference/WP_Query#Custom_Field_Parameters

This tag “$query = new WP_Query( ‘meta_value=Cincinnati’ );” sounds like I am in the right direction, but how do I use it in the theme?