Skype, now owned by Microsoft, does have an app for the iPad. You can find instructions for getting started with it on the Skype site.
One of the biggest advantages Skype has over Apple’s FaceTime app is that you can make audio and video calls to other Skype users around the world on more types of hardware. This includes calling Windows and Mac computers, Android devices, Windows Phone handsets and even certain Skype-enabled televisions and Blu-ray players. Skype-to-Skype calls are free, and for a bit of money, you can call regular telephone numbers.
Apple’s FaceTime app is also free for one-to-one video calls, but it only works on certain Apple-made products. These include camera-equipped iOS devices made within the past few years and Macs running OS X 10.6 and later. Still, because it is integrated into the operating system, FaceTime can be a little easier to set up and use if you plan to chat only with people carrying Apple gear.
Video and audio quality in both apps may vary based on network and data traffic issues, especially if you are calling over a 3G or 4G cellular connection instead of Wi-Fi . Since both apps are free for video calls, there is nothing stopping you from using both as you need them — or even adding Google+ Hangouts into the mix if you are a member there, too.