The standard applications do not offer some of the functionality you need. The R/3 enhancement concept allows you to add your own functionality to SAP's standard business applications.
SSCR (SAP Software Change Registration) is a procedure, for registering all manual changes to SAP source coding and SAP Dictionary objects.
Adding functionality to R/3 applications. Function module exits play a role in both menu and screen exits.
Customer exits are not available for all programs and screens within the R/3 standard applications. You can only use exits if they already exist within the SAP R/3 System . Otherwise you have to opt for modifications.
Add documentation to the data elements of key words defined in the ABAP/4 Dictionary. The system displays this documentation whenever a user presses F1 to get online help for a screen field.
Customizing is the setting of system parameters via SAP's own interface.
Creating customer-specific objects within the customer name range.
Enhancements using customer exits:
Adding items to the pull down menus in standard R/3 applications.
SAP organizes its exits in packages that are called SAP enhancements. Each SAP enhancement can contain many individual exits.
Adding fields to the screens within R/3 applications. SAP creates screen exits by placing special subscreen areas within a standard R/3 screen and calling a customer subscreen from within the standard dynpro's flow logic.