Computer Binary Usage

I learned that there is no decimal usage. For example, they consider every number 1-2 as 1, any number 2-3 as 2, and so on. I also learned that an analog signal is a signal that is proportional to the value it represents. Also, binary numbers are longer than any other form of writing the number. I don't understand why two is such a special number. I also don't understand how high voltages and representing them with a wire is dangerous. I would like to know more about representation of voltages and why they are dangerous but also important.