Typically, in forms with a single submit button, you could simply say form.submit. This is by far the most common way of submitting forms. It will build the POST or GET query, perform the query and return a new Mechanize::Page object.
If there are multiple submit buttons, you can "click" on a specific button by passing that button as the first argument to the submit method. For example, if there is a button with the text "Google Search" as well as a button with the text "I'm Feeling Lucky", you could do the following.
#!/usr/bin/env ruby require 'rubygems' require 'mechanize' agent = Mechanize.new page = agent.get('http://www.google.com/') form = page.form_with(:action => '/search') # Set the 'q' field like this form.q = "Ruby Programming Language" # I'm feeling lucky! page2 = form.submit( form.button_with(:value => "I'm Feeling Lucky") ) puts page2.title