Turn on Skype in Outlook

Go to File > Options and select Add-ins in the left pane.

Select Skype Meeting Add-in for Microsoft Office under Inactive Application Add-ins. 

At the bottom left next to Manage COM Add-ins, select Go.

In the Com Add-ins dialog, scroll down and select Skype Meeting Add-in for Microsoft Office.

Select OK. In the calendar you should see the New Skype Meeting button.