This is important to know before you commit to an online program, because some piano systems require special tools or plug-ins to be able to use certain features.
A good program should be mindful of using tools that are commonly available to all users. For example, printable pages should be in pdf format, audio clips should be in mp3’s, and videos should be easily viewed on computers as well as mobile devices.
And, of course, the obvious… you will need a piano or keyboard!