If you don't have IDroo, get it from here. Otherwise, start it up from the Desktop or Start menu.
Also make sure you have Skype running.
Allow access to the Skype API
On first use, you will be asked to allow IDroo to access the Skype API. You should see a notification in Skype. Click on "Allow access". If you don't see the notification then you might have allowed access already.
Now you can invite others to collaborate or start drawing on your own. Browse other documentation pages for more tutorials.