Data is often used to represent concepts, objects & systems in the real world. Computers represent everything (i.e. both data and instructions) as sequences of bits (short for binary digit), whose values (like a toggle switch) can be either on or off; we use off to represent 0 and on to represent 1. We can group these bits into larger and more complex structures to represent anything we want them to.
The easiest things to represent are dichotomies (e.g. true/false, yes/no, up/down, north/south, etc.) because it takes only a single bit to represent them. We call these booleans (in honour of George Boole, a British Mathematician & Philosopher).
Next up are numbers.