lets start with the basics binary is a number is made up of only 0s and 1s.For example 1011. Ok to us in decimal is one thousand and eleven. But in binary its completely something else.
128 64 32 16 8 4 2 1 1011 in Binary we use a table. The table represents how many bits there are. For example if we put a 1 in the colum 2 and and 0 in the collum 1 the total bits would be 2. So we put the number 1011 in the table. We can see that there are 8 bits plus 2 bits plus 1 bit. The equation here is 8+2+1=11. The reason why we didnt add 4 is because these is a 0 therefore there are no bits.