
best place to start is look at source code of PG
right click, view page source
that being said,
start from here, they will hold your hand, guide you.
get more aggressive, download apache server on your PC. Build websites with databases (trust me, its easier than it sounds.)
Once you are comfortable in that, move to real web hosts, see what you created.
Experimenting and learning, thats the key.

i forgot, coursera. check out them.