Which is the best guide to learning php. I mean at the simplest level.
for some who dosent know anything about programming.

I'd recommend W3Schools.org for novice learning - once you've got the hang of reading (and not necessarily writing) PHP code, check out an Open Source application (I started with OS Commerce) and review the code.

You'll pick up the syntax @ W3Schools and then you can see some practical application in a working app (not to mention some useful script architecture examples).

^Thats the best thing to do, but some experience with a language such as HTML would help a lot. This will just help you understand how programming and everything helps.

I am infering that you do not currently know any other languages. If you do, sorry!