You will need to click the 3 lines at the top of the page, click on Platforms, and then click on MetaTrader4 or MetaTrader5.
Then scroll down a little until you find MetaTrader all devices and click on Mac (If you are using an iPhone/iPad, click App Store.
The MetaTrader website suggests:
Play on Mac: Click here and follow the instructions.
Live server details are: mt4.NashMarkets.com
Demo account details are: demo.NashMarkets.com
We do not officially support Play on Mac.