There are several ways you can create programs that use your DP4 databases. For an overview see DP4 Programming Tools in the Introduction to DP4.
To learn about programming using C and C++ refer to the DP4 C/C++ Programmer's Reference.
To learn about programming using QA Build, or QA Build with C refer to the QAB Developer's Manual
To learn about using Report Writer to create Reports refer to the Report Writer Developer's Manual
To learn how to export information from your DP4 database so that it can be imported by other programs/systems and how to write Importer programs to import data from other systems refer to Copying Data between Databases in the DP4 Developer's Manual.
To learn about using SQL, or connecting to DP4 databases from other products via ODBC, or connecting to other databases from DP4 programs refer to the DP4 SQL Products Guide.