php - How to use option lists to change POST value? -

I have a gallery page that changes the category based on $ _POST ("cat"), how do I change I can use

Here is the options list:

  & lt; Form & gt; Click on the page. & Lt; Gt selection and; & Lt; Option value = "" & gt; Choose a category: & lt; / Options & gt; & Lt; Option value = "1" & gt; Landscape & lt; / Options & gt; & Lt; Option value = "2" & gt; Marriage & lt; / Options & gt; & Lt; Option value = "3" & gt; Miscellaneous & lt; / Options & gt; & Lt; / Select & gt; & Lt; / Form & gt;  

This is the pH option list:

  & lt; form action = "gallery.php" method = "post" & gt; select