from what I searched on the internet, I know:
but I am not sure which language is executed first. is there a process flow?
and, did I left out any element(language) of a webpage?
So, the process flow of a website is very close to what you have. I'll run you through an example website access so you can understand it.
A Page Request
The user requests a page from a web server. The web server, receives the request, and prepares to send the requested page to the user. If the server is setup to do so, it will run a server side language parser and execute the page so that it knows how to process and serve the page correctly (PHP is a common example, as is PERL and ASPX). That code is executed and will often times output a page to send to the user (you can also do this for documents, and other things as well, but we're talking about a page here.
Languages and Their Uses
There are also a lot of other web technologies that exist besides the ones explained here. For example, many servers often contain databases to store data on the server (like users, news articles, etc) for presenting different information at different times. If you are interested in learning these things, I would recommend doing some personal research, maybe going through some tutorials (the ones at W3 Schools are good), and possibly signing up for some classes maybe at a local college. Personally, I learn by doing, so for me, the best way to learn was to just start playing around with things and seeing what worked and what didn't. And this place, as well as sister sites like StackOverflow are a great place to ask questions and learn.
Hope this helps. Stick around, and if you have any other questions, feel free to post them. Good luck =)
UPDATE: A User's Interaction with the Database
So, a user can interact with a database in a lot of ways. The first, is simply by hitting a page. A lot of servers track page visits, and user statistics by recording certain information about users when the request a page. By this I mean that when a user requests a page, they have to send a lot of other information to the server other than just the page name. The internet is a big place, so they have to send information about whom the server should respond to, what browser they are using (though this can be spoofed), and a lot of other information. Now, one of the other ways the user can interact with a database is with all of this information that gets sent. On a web page, a user can fill out forms (like the ones here) and choose to send that extra information to the server along with their request for a page. This information is then what is used to add comments, update information, or answer questions.