You can use your PC, mac or windows, also Linux, PHP is really what you want to learn, the codex, is probably the best place to learn however it is not really friendly, it is sort of the Nerd version of an Oxygen bar.

Writing a Plugin « WordPress Codex

There used to be a product on here, by Robert Plank, but I think it is a little out dated now with the latest versions of wordpress and PHP, there really is not a lot to it, but the best method of learning how to do it is to go to the wordpress directory and download some plugin and start examining the methods that they use, a background in PHP is going to be very useful here, if you do not know PHP that is where I would start because without some useful knowledge about how PHP works, you will be lost trying to follow those nerds, at the codex,

Hope that helps set you in the right direction.

You might also be interested in Wordpress plugin development course on Lynda.com. It's 3 hours and 51 minutes long and the quality is top notch (as always on Lynda). Unfortunately it's not free though, the subscription is 25$/month but you'll get access to all the video courses so it's worth it.

I hope this helps!

Honestly, I found the fastest way to jump right into it was to download a plugin that has the functionality I'm looking for and just read through the code of that plugin. There is a simple Wordpress plugin included in every install called "Hello Dolly" (basically a slightly more complex Hello World) that you can look at to get a grasp of the absolute basics.

A cool thing about Wordpress plugins is that you can organize them however you like in your own little directory in /wp-content/plugins/my-plugin/ and you don't necessarily have to follow the Code Styling guide that the Codex suggests.

I guess the big things to wrap your head around are:
* How do I execute a function at a certain part of the page w/o modifying WP core files (See action hooks)
* How can I modify something that Wordpress has generated w/o modifying WP core files (See filter hooks)
* Avoiding conflicts with similar named plugin functions (Avoid by prepending something unique to your functions eg. warriorplugin_myfunction(){ instead of myfunction(){)

Simply put, you can develop your entire application standalone, and then pop every individual view that you want to display into it's own, separate function and use an action hook to latch onto specific parts of the page as it's executing.

Good luck!