I have some very simple advice for you, to get started on a minimum budget:
1) Use Garageband. it's free with your mac! Eventually you can upgrade to Logic (fantastic for making electronic music, and a great value too) but stick with Garageband for now (because it's free, and if you get Logic later, you can import all your Garageband projects into it!)
2) Buy a basic midi controller of some kind. You can get a good basic one for $100 or $200. The KIND of midi controller depends on your musical style and abilities. I would suggest a simple keyboard controller, like the M-audio keystation series. They offer fantastic value. It might be nice to get one with knobs or faders, but getting a basic keyboard controller will absolutely suffice (and will cost less)
3) Learn some theory and techniques on playing and composing music, as well as audio recording on computers (e.g. using DAW's (digital audio workstation, which includes Garageband). For this, you can talk to people you know if they possess these skills, or take lessons, but the internet has TONS of free lessons and advice and tutorials. Look on youtube, look at websites like soundonsound.com, download some free e-books, etc. You can buy some good magazines too (e.g. computer music, future music, etc.). There are many free or cheap resources for you to draw upon.
Although I learned how to play music as a child, I started making music with an old windows computer, but I really got into it when I bought a Mac that had Garageband on it. And now, I make music using a variety of programs (mostly Logic and Ableton).
You can totally do this, and you can totally do it cheaply too! It's fun living in 2013! If you have more questions just ask!