Cees-Jan Kiewiet has a post on his site focusing on the HTTP client side of the functionality offered by the ReactPHP. In this post he covers the basics of installation and usage with plenty of code examples (and screencasts of it in action).
Aside from a HTTP component ReactPHP also has a HTTP Client component that lets your send out HTTP requests. It is incredibly handy when you need to communicate with for example elasticsearch's REST API, AWS platform through their SDK or the RIPE Atlas API.
He walks you through the simple installation of the library (via Composer) and the code to send a simple request to an
example.com domain, returning the HTML contents of the page. He then gets to some more complex examples: sending two requests at the same time, streaming the response body as it arrives and an example based on community feedback - streaming Twitter data. He ends the post with a community example showing the use of the Buzz HTTP client to make simple requests.