Key Takeaways:

The WordPress HTTP API simplifies making remote HTTP requests: requests for information that return (and may also alter) webpage content using HyperText Transfer Protocol (HTTP), the fundamental means of communication on the internet.
The wp_remote_get(), wp_remote_post(), and wp_remote_head() functions make GET, POST, and HEAD requests, respectively. wp_remote_request() can make all forms of HTTP requests.
The HTTP responses received as the result of HTTP requests are further processed by response handler functions. Prewritten handler functions, such as wp_remote_retrieve_body() and wp_remote_retrieve_header(), greatly simplify parsing many responses.

From time to time, you'll need to call remote resources—resources on sites other than your own. A common way to do this is by making HTTP requests for the information you need. This chapter explains HTTP, and digs into WordPress's HTTP API.

Understanding HTTP
The web works through HTTP: HyperText Transfer Protocol. H...