Requests and responses in the HTTP protocol

Let's say a user wants to open a page of a website in a browser. To do this, the user either follows a link or enters the URL of the page into the browser's address page. Both methods are technically equivalent.

The browser then sends a request to the server, asking the server to return the page at the specified URL. The server receives the browser's request, forms a response and sends it back to the browser.

The request and response are simply strings formatted in a special way. The rules for formatting these strings are governed by the HTTP protocol.

Thus, all interaction between the client and the server is reduced to throwing messages back and forth, like balls in a game of ping-pong.

In this case, the request initiation is mandatory. This means that the server always sends a response to the browser's request. It cannot be that the server sends something to the browser itself, without a prior request from the browser.