If you ready to work on 4-1: Search Engine, watch David’s videos below and follow along in cloud 9. He explains and types in the code to create a form and a get request to google. You can follow along in cloud9 to create your own form and get request, and then style it using css.
First is the lecture video from fall 2015, where he develops his code in cloud 9. Starting at the 29:00 point, until about 36:00, he builds a search engine front end. After this he demonstrates using CSS to style his page.
These short videos below, break down the process a bit further. These were created before CS50 used cloud9 so the previewing process is a bit different.