All information exists in computers in the form of electrical voltages. The voltage represents a binary number; 0 volt is a binary 0, larger than 0v is a 1.
So hexadecimal values each describe a "set" of binary values, which in turn are represented by voltages on wires. For example, the hexadecimal digit "a" means 1010 in binary, which could live on a computer data bus on 4 wires.