im confused, what exactly is the point of php?

ok, ive seen some websites with php extentions, teamphotoshop included. i just want to know what exactly is the point of useing that extention, and what will it do for you that javascript and html wont? please let me know cause i hear its really cool! heheh
later.

It's used for web programming, databases and stuff. This board was made with php. But on the sites is probably used for the include command (and because it's looks cool and professional wahaha)

include command works as ssi does i think.