Pages are basically some data served by a web server (like Apache, nginx or IIS) in response to a request. When you type (http: //wikipedia.org/something/etc) in your browser, the browser locates the server (identified by IP address) associated with that domain, and makes an http request on one of its ports (default port 80 for http, 443 for https) for the specific url you typed. This can be a file on the disk, or some information in the database, or data in the cache of the serving computer, but you need to tell the server how to process the request and what data to return. Otherwise the server will return a 404 status code in response, which means "Not found".
The browser can also POST data with the request. This is what happens when you submit a form (using HTML form elements). The form will have an attribute called "action" - and this is the link to which the browser will try to submit the data in the form. Again it is up to you to have something set up at the server-end to receive that data, process it by saving it into a database or a new page, and sending back a response page.
So when you visit Wikipedia, you are not directly doing any of this because Wikipedia's programmers have taken care of all this. Their scripts on the server-side receive the posted data and use it to create new pages or make changes to existing ones.
This is the very nature of programming: setting something up to take care of certain actions in specific ways, leading to specific results as you wish.
