Computers deal with powers of 2. They read data as two states, either 1 or 0, calles binary. But you need to create chuncks of data. So 4 bits is a nibble and 8 bits is a byte. We mainly deal with bytes in storage computations.

So 2^2 = 4, 2^3=8, 2^4 =16…2^8 = 256, 2^10= 1024.

So if we represent that using metric system of base 10 decimal. People tend to say 1KiloByte ( 1000 bytes), but a computer sees 1024bits due to the power of 2 groupings.

Man i suck at ELi5, hope that made any sense.