What are the advantages of structures? How do you use them in the ABAP programs?

Using a structure, user can add fields to the existing SAP database tables. Using .INCLUDE and .APPEND statements structures can be added to the database tables. Creating structures with in a structure is also possible. User can add maximum 9 structures to a database table. Structures are used to hold data from tables during runtime of a transaction or a program. It can be applied in programs by the FIELD STRINGS.