Filtering a page by custom fields

Filtering a query on the value of a Custom Field is certainly possible. See this Codex article on Custom Field Parameters: http://codex.wordpress.org/Class_Reference/WP_Query#Custom_Field_Parameters

Allowing viewers to select the value of the field is a different problem that can require quite a bit of code. Here is an article that shows a basic form for the Twenty Ten theme that lets a viewer select a Category and a sort order: http://wordpress.mcdspot.com/2012/09/21/simple-form-to-select-a-category-and-sort-order/