Hi helloise,
What you are trying to achieve is simple, and there is even a name for it: AJAX.
However, if you are starting in php, html and javascript, asking in a forum will make you go very slowly.
I recomend that you start reading http://www.w3schools.com/
It covers all the topics that you mentioned plus lot more.
Programming can lead to frustating paths, but it is a lot of fun to see things working, either on a web page or an application.
Good luck, I know that anybody can do it.
--
Jorge