Encoders convert decimal input to binary coded decimal (BCD) output, while decoders convert BCD input to decimal output displayed on a 7-segment display. An example encoder converts decimal numbers to their BCD coded form, while an example decoder converts BCD codes into the decimal numbers they represent, which are then shown on a 7-segment LED display. The document provides examples of encodings and decoding between decimal, BCD, and 7-segment display representations and tests the reader with questions about decoding BCD inputs.