The coefficient     is multiplied by   and it is known as  most significant bit (MSB).
The coefficient              is multiplied by        and it is known as  least significant bit (LSB).

For our convenient, while writing in paper, we may take help of other number systems like octal and hexadecimal. It will reduce the burden of writing long strings of 0s and 1s.

Octal Number : The octal number system is said to be of base, or radix 8, because it uses 8 digits and the coefficients are multiplied by power of 8.
Eight digits used in octal system are:   0, 1, 2, 3, 4, 5, 6 and 7.

Hexadecimal number : The hexadecimal number system is said to be of base, or radix 16, because it uses 16 symbols and the coefficients are multiplied by power of 16.
Sixteen digits used in hexadecimal system are:  0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E and F.

Consider the following addition example: