I have been to the Office365 website and looked in the software section but I cannot find it.
Any assistance would be appreciated.
Microsoft has officially released Skype for Business for Mac on October 26th, 2016. You can find the official download link here: https://www.microsoft.com/en-us/download/details.aspx?id=54108
If you are using Homebrew (and Cask), you can install Skype for Business for Mac with the following commands:
brew update ; brew cask install skype-for-business
Skype for Business has not yet made it in full to the Mac.
Microsoft are instead still offering the older Lync software...
Set up Skype for Business (Lync) for Mac 2011 for Office 365
If your organization is using Skype for Business (Lync) for Mac 2011, you can use it with your Office 365work or school account.
To use Skype for Business (Lync) for Mac 2011 with Office 365 you need to go to the Office 365 portal and click Install Skype for Business (Lync). Note: The Install Skype for Business (Lync) button will only be available if Skype for Business (Lync) was part of your plan and if it has not already been installed.
If you haven’t installed Skype for Business (Lync) for Mac 2011 yet, you can install it from this location: Skype for Business (Lync) for Mac 2011.
It's due for release in early 2016 apparently but in the meantime, Lync 2011 is basically Skype For Business.