Contact form 7 is one of the best contact form generator plugin available for WordPress today. It is created by takayukister and the best thing is, the plugin is free for everyone who is building their site in the WordPress platform.
Sometimes, you may need to redirect users after filling up and submitting the form to achieve superb user experience on your site i.e.: Free audio, free ebook, free download etc.
//Obviously, you need to change http://example.com/ to your desired URL. on_sent_ok: "location = 'http://example.com/'"
Thats it and you are good to go.