If you want to use your Oracle Form's functionality in Oracle Apex application then you need to convert first Oracle Form into XML using frmf2xml utility in Oracle Forms 11g and then you need to create a migration project into Oracle Apex.
Below are the steps are given to perform this task.
1. Convert Oracle Form to XML using frmf2xml.bat
Run the frmf2xml.bat by providing your FMB file with its location from the Oracle form's instance home directory as shown below:
It will convert and save the XML file into the same location of your form.
2. Create an Oracle Apex Workspace.
Run Oracle Apex and create a workspace with the same Oracle Forms application schema.
3. Create a migration project in the workspace you created. App Builder > Migrations
Log in to the workspace and create the migration project and import the XML you created.
4. Create the Oracle Apex Application and Associate with the Migration Project.
Create a new application using in Application Builder and then go to App Builder > Migrations and edit your project and associate the project with your new Apex application.