> Can i use Language like PHP ? or what ever you think that easy to learn ?

There are many languages out there like Java, Perl, PHP etc. Pick any one of them and start learning though PHP seems to be the easier choice here because of its widespread use.

> I am not sure what kind of change would be unless change like example :
> In the file2 change a background because file3 got click on his page .
> example :
> Change file3 his one element ID , because file2 and his pal file1 got name from the user .

You can do all that and much more once you start off with server side programming. These server side technologies impart dynamic nature to the otherwise static pages and so changing the background color of a page based on a click on another page and much more complicated things are possible.