Vortex Sound Research

Firstly sorry if this a very obvious question, I’m new to the music production scene and am doing this purely for fun with no intention of making my music public. I have a DX7 and am using a MacBook with Garage band (yes I know it’s not as featured as other applications but it’s free and easy to use and this is just something I’m doing for fun).

Where should I start? I’ve tried hooking the audio out to my mic input on my MacBook and it didn’t work so I’m assuming I need some other piece of hardware. My budget is <$150.