Php scripts will be entire libraries or even blocks of functionality that you can (in theory) use. I wouldn't recommend going down this route unless you know what you're doing, because there are far more poorly written scripts out there than good ones. You'll end up with an incoherent mess quite quickly if you just attempt to stick a bunch of scripts together.
From scratch is obvious - just write stuff yourself from the ground up.
Frameworks are a different thing altogether - there are many frameworks, but generally the principle is the same - they tend to have lots of (usually well written) code that helps you from having to re-write stuff that happens a lot in general web applications, and leave you to write only the code that is unique to your application. So for example, you may use some of their code to deal with user permissions and user authentication, without having to re-invent the wheel and write it all from scratch yourself.
However, with Frameworks comes a learning difficulty (all frameworks are different, although most generally follow what is called the MVC (model view controller) pattern. You will also generally need to know how to write Object Oriented code before you really start working with a framework.
So generally, I'd recommend starting by writing from scratch to get the hang of the language. You will make mistakes. You will find your code becomes hard to change over time and stuff may stop working. You'll find sometimes you'll change something somewhere and it'll break something somewhere else that you hadn't anticipated. All this stuff is good for you though because you'll start to learn what things work well and what don't, and over time I'd recommend THEN moving to a modern framework such as the Zend Framework or Symfony 2.
Don't expect to get rich by making your first website. You'll make mistakes on your first site and you'll almost certainly scrap it in the future when you start to get better (if you persevere).
As Victorialpx mentioned above, a good resource is http://www.phptherightway.com take a look at that for some good advice and starting points too.