Example:

//Instantiating a Workbook object
Workbook workbook = new Workbook();
 // Init VBA project.
VbaProject vbaProject = workbook.getVbaProject(); 
// Add a new module.
int index = vbaProject.getModules().add(VbaModuleType.CLASS, "test");
// Get vba module
VbaModule vbaModule = vbaProject.getModules().get(index);
// Set codes
vbaModule.setCodes("Sub ShowMessage()\r\nMsgBox \"Welcome to Aspose!\"\r\nEnd Sub");
//Saving the Excel file
workbook.save("C:\\book1.xlsm");