Many raw measurements result in analog data. For example, when a microphone measures the sound pressure level to create an electric wave, the signal is analog. However, the majority transmission / storage of information is done digitally. Anything saved, transmitted or processed using a computer, or stored of DVD, CD, flash media etc is done so in digital format.
The slides outline how an analog wave is converted into a digital wave, and mention some examples of digital communication (blu-ray, mobile phones, modems and hard drives).