Use for web development is making real websites. What Xampp does is combine a standard group of applications in one bundle that you will need to build dynamic website/s and test its functionality (development). It includes amoung others; PHP, a server side scripting language; MySql for databases and Apache server. It also includes phpMyadmin to help manage your databases.
May I also suggest - if you don't have a text editor made specifically for creating websites then consider Komodo Edit (free), TextMate, or BBEdit (if you have bucks). You can use the regular textedit that comes on the Mac, but some of the features of these other softwares will make it easier to write the code - using syntax coloring, highlighting and line numbering (extremely handy). I use TextMate - nice and affordable.
Anyway, you can browse the threads for answers to questions, solutions to problems or like you just have, just ask - see you around.
edit for clarification:
PHP is what language Drupal is processed to, so you will need PHP to run it. Since Drupal uses databases to store what will eventually be quite a bit of information, you'll need the MySql database. There are quite a few ways to manage the databases, ie., Terminal (a little clunky unless your a Mac Nurd) or, basically the same thing, MySql's that runs through the terminal or a fairly easy to use GUI called phpMyadmin. There are more out there, but I don't keep up with them.
The idea; get it working on your development machine, then transfer it to your production server, yours or a hosting server- online.
The Mac, depending on your version comes with Apache and PHP if you want to serve your cms from your computer. You will just have to load and configure Mysql and probably add something like phpMyadmin.
If this is more than what you needed - overlook it.