couple of questions about css and php

for about a year now i have been reading tutorials online and have learned a lot
i know most html (its not hard really is it) and a little php/mysql
if there is something i need from php there is usually a nice site that kindly offers a copy and paste of script for me, so no problems there. and i have no problem editing it and playing with it to mould it for my requirements

obviously i try to make sites SEO, which is the main problem i find. i read a great tutorial on css or php only to later read elsewhere that it wont be very good for SE or has problems for other things.

its confusing with all the tutorials out there to know if what i am learning is the 'best' way.
so i though where better to ask a fer things than here

where can i find a tutorial for drop down navigation menus in css and html (not java as i believe its not good for SE) that have both horizontal menus on the top and vertical menus down the side on one page?
like many great sites have.
i can only find ones with vertical OR the horizontal, and have tried for weeks to play with the code myself to get both working on one page, with no joy.
and there seems to be many different ways to acheive the same thing in css. again, i make something one way to read later that i shouldnt have done it like that.
if you can provide a link to a decent site it would be appreciated, and any other sites that offer good tutorials

also is it ok to create web pages with .php extension that has html in it even though there is no php?
some of my pages have php and some dont, and i found it easier to just make them all php
what is best practice for this? i.e. the ones without php make them .html, and the ones with php make them .php
i read a lot that for beter SEO they should all be one type?

and are there any good tutorials that go through a full page creation? rather than the only ones i find which seperately cover each tutorial and you have to try to piece it all together your self

lots of text, sorry
many many thanks in advance!!