How to connect a mic to the macbookpro will depend a lot on what kind of mic… Do you already have one? Or planing on buying one?
Some computers have a shared mic/line input, but apparently on recent macs they only come with line-in. Therefore you’ll most likely need a preamp. Which one to get will depend on the mic you’re going to use with it (whether you need phantom power or not, etc…)
One of the cheapest I’ve seen is T-Bone’s micplug, which is an XLR to usb device, powered from the usb and provide phantom power. The quality of the miclug is not that good though.
ART preamps are usually well regarded here on the forums.