create a filter dropdown with a custom query

hi everyone…
i need to create a filter dropdown to show post in a custom page. i’ve revised this page, which cleared few doubts about to how query in the database.
but i need to create a dropdown with the custom column value inserted in the post, recall the page, and show the post filtered by the dropdown.
the questions are:
1. how create the dropdown to show in the page?
2. how i do to pass the parameter selected to the page?

or tell me in which pages found information about this..
thanks..