You have a good point Jasonsmith21! 'Cause php for instance, would be more appropriate. But..... in that case I have to go back to school, because I don't know anything about php.
PHP is an extremely popular server-side language, there are plenty of online tutorials, such as on Code Academy and the handy Code Igniter (if you choose to use it).
For your initial question, HTML and CSS are client-side, so anyone can change it, however, it's possible that by changing certain things, it won't work (just need to refresh the page in that case). If you mean by permanently changing text in the webpage for everyone to see those changes, then you'd need access to the actual source files and server/host providing it.