When you see a number like , its binary representation is . Reading from right to left, the positions represent , and so on.
For : position 0 has a 1 (worth ), position 1 has a 0 (worth 0), position 2 has a 1 (worth ), position 3 has a 1 (worth ). Total: .
I number bit positions starting from 0 on the right. The rightmost bit is position 0, also called the least significant bit (LSB). The leftmost bit is the most significant bit (MSB).