Skype for Business is a powerful communication platform that is used for online meetings and instant communication. Skype for Business installs as a client on your device, and is then used in conjunction with other Office 365 apps (such as Microsoft Word, Excel, PowerPoint, and Outlook) or as its own communications device.
If you're familiar with Skype, then you're already familiar with Skype for Business. Skype for Business is just a business version of Skype with the same great features.
Skype for Business used to be called Lync. Microsoft acquired the Skype consumer product and dutifully has been merging it with the Microsoft Lync product to leverage the best of both products.
Skype for Business uses a high amount of bandwidth for communication using voice, video, and screen sharing. For these reasons, you should plan on a fairly fast Internet connection to ensure a good experience. Skype can be used on your iPhone with regular 4G cellular service all the time without any problems. If you're on a slow connection, your mileage may vary.