You can already conveniently send money via PayPal or Venmo through other apps. PayPal has a Slack bot that lets you transfer funds through chat and you can Venmo money through iMessage. You can even ask Siri to send some cash through PayPal for you.
To send money through the app, you'll need to have the latest version, but the person receiving the money can have any version of Skype. You'll both have to have PayPal accounts and live in one of the 22 countries where Send Money is currently supported. But, as usual with PayPal, you have the option of sending funds in different currencies if need be.
The countries that support Skype's Send Money feature are the US, the UK, Austria, Belgium, Canada, Cyprus, Estonia, Finland, France, Germany, Greece, Ireland, Italy, Latvia, Luxembourg, Malta, Netherlands, Portugal, San Marino, Slovakia, Slovenia and Spain. The service is rolling out starting today.