Installation on a Mac

[Siephe]

I noticed that there was a child board for Windows and Linux, but what about a Mac? I'm a complete beginner to PHP and I'm not sure on exactly what to do to get PHP up and running locally on my computer. I've been reading a lot online about it, but let's say I'm a bit slow and still unsure.    So I've got a few rather stupid questions, but well, here we go:

 

1. How do I install, or upgrade my version of PHP on a Mac. What do I need to be able to run and test it locally?

2. If I do run and test locally, will it affect my system if I make mistakes or whatnot?

3. How does it all work?

 

I've only got experience with HTML and CSS. And I would love to get started on PHP! Thanks!