Bit
Smallest unit of information a computer can store. 1 or 0.
Code
Association of sequence of bits with information.
To make sure everyone interprets the code in the same way, standards such as ISO, IEEE are created. Different standards are defined for different data types.
Common standards
ASCII
Uses 7 bits for a code. Unique combination for per English character. Includes both printable and unprintable characters.
Unicode
Uses 32 bits for a code. Designed as the superset of ASCII.