Understanding binary numbers is important. All things digital involve circuits and systems in which there are only two possible states. Two voltage levels represent these states; a HIGH and a LOW. In other words, digital devices communicate this way. For a quick review on what it means to be digital, check out the post Analog vs Digital: What’s the Difference?
Binary information that digital systems work with appear as waveforms that represent a sequence of bits. As an example, see the figure below which relates the 1’s and 0’s to voltage levels on the waveform A. As we can see, a 1 is a HIGH and a 0 is a LOW.