Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Yosemite is OK for Skype versions over 7.x and can be gotten from the Skype for Mac on this page:
Install that after downloading it to your computer.
Make sure that the camera shows up in the Dock (maybe) or on the Desktop as a device, before expecting it to work.
Let me know if you have difficulty at any point, and I will advise you further.
(Be sure to configure the camera settings in Skype.)