I ran into this issue (randomly) about a month ago and ultimately I had to uninstall Skype and remove all the library support files, then reinstall/reconfigure to fix the issue.
If you still encounter issues, check out Skype's client for Mac support forums (as well):
The "~" stands for your user library or home library. But it's now hidden by default. So the easiest way to get to it would be this -
1.) Open Finder
2.) Hold the Option key on your keyboard
3.) Click on the "Go" option in the top Finder menu bar. It's important you're holding the Option key when you do this, otherwise the Library option will not be visible.
4.) Click on Library and this will get you to the ~/Library phase, you can now release the Option button. The folders are usually alphabetical so Application Support will be at the top.
Skype Installation FAQ - https://support.skype.com/en/faq/FA79/how-do-i-install-skype
Skype Download URL - http://www.skype.com/intl/en-us/get-skype/on-your-computer/macosx/
It's a pretty straight forward process. Download the installer, run the installation app, unmount the installer when completed.