how can i download majic jack onto my mac book

Depending on what MacBook build model, year, configuration

(software/hardware) you may be able to use some application

to make internet calls, this may require headset w/ microphone

or other specialized gear. And that may also be a bottleneck.

Also, the internet speed via your ISP could be an issue, too.

A few legitimate sources of sofware are out there, even so,

be wary of click on links to adverts that could install malware

or badware for purposes of their own... Both appear here:

https://www.google.com/#q=Mac+OS+X+free+phone+calls+application

Some legitimate software applications for this require certain

systems to be running, and those require hardware specs of

a level necessary to support the system needed, and so on.

As I've never used those, I can't say I prefer any of them...

Good luck & happy computing! 🙂