Actually we start with zero, not one.
The binary system position are powers of 2.
i.e. (binary = decimal)
0 = 0
1 = 1
10 = 2
100 = 4
1000 = 8
10000 = 16
100000 = 32
etc.
Each position, in binary, is a power of two (as in decimal, each position is a power of 10).
11 = 3
101 = 5
110 = 6
111 = 7
BTW, IPv6 uses hexadecimal where each position is a power of 16
1 = 1
10 = 16
100 = 256
and
11 = 17
.
.
1F = 31
.
.
FF = 255
If this still doesn't make sense, try searching the Internet, for primers, on different number bases, especially bases 2, 8 and 16.
PS:
Personally, "entering" networking from a programming background, I was surprised to see IPv4 used dotted decimal rather than hexadecimal, as computer addresses were often represented in hexadecimal, sometimes octal. The decimal representation, I believe, makes it a bit more difficult to understand shifting bit positions for understanding network vs. host allocations of a network address.
