If you are just getting started with a Demo account, I would suggest downloading ThinkorSwim by Ameritrade.   They have a great free platform and the best part is it runs on a mac.

There are a few drawbacks relating to delayed quotes, but for the most part a new trader is not going to find a better platform, and it's hard to beat FREE.

Click here to Visit their site and check it out.

Most of my trade pictures will be taken from this platform.